update edition guide

[steveklabnik]

spiritual successor to #56457

not to be backported, being in nightly is enough.

i'm testing this locally now but figure travis can test it in parallel

[rust-highfive]

r? @frewsxcv

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[rust-highfive]

The job x86_64-gnu-llvm-5.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:180e89aa:start=1543960784351667664,finish=1543960785390121340,duration=1038453676
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#Pull-Requests-and-Security-Restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-5.0
---
    100% |████████████████████████████████| 1.4MB 845kB/s 
Collecting botocore==1.12.59 (from awscli)
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
  Downloading https://files.pythonhosted.org/packages/21/cf/71dfc14692883aaf709bc1098a56770173a760a14b0b1cb74471609181be/botocore-1.12.59-py2.py3-none-any.whl (5.1MB)
    0% |                                | 10kB 35.6MB/s eta 0:00:01
    0% |▏                               | 20kB 31.7MB/s eta 0:00:01
    0% |▏                               | 30kB 36.8MB/s eta 0:00:01
    0% |▎                               | 40kB 28.9MB/s eta 0:00:01
---
###############################################################           88.2%
######################################################################## 100.0%
[00:01:21] extracting /checkout/obj/build/cache/2018-10-30/cargo-beta-x86_64-unknown-linux-gnu.tar.gz
[00:01:21]     Updating crates.io index
[00:01:28] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:28] Build completed unsuccessfully in 0:00:32
[00:01:28] make: *** [prepare] Error 1
[00:01:28] Makefile:81: recipe for target 'prepare' failed
[00:01:29] Command failed. Attempt 2/5:
[00:01:29] Command failed. Attempt 2/5:
[00:01:29]     Updating crates.io index
[00:01:30] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:30] Build completed unsuccessfully in 0:00:00
[00:01:30] Makefile:81: recipe for target 'prepare' failed
[00:01:30] make: *** [prepare] Error 1
[00:01:32] Command failed. Attempt 3/5:
[00:01:32] Command failed. Attempt 3/5:
[00:01:32]     Updating crates.io index
[00:01:32] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:32] Build completed unsuccessfully in 0:00:00
[00:01:32] Makefile:81: recipe for target 'prepare' failed
[00:01:32] make: *** [prepare] Error 1
[00:01:35] Command failed. Attempt 4/5:
[00:01:35] Command failed. Attempt 4/5:
[00:01:35]     Updating crates.io index
[00:01:36] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:36] Build completed unsuccessfully in 0:00:00
[00:01:36] make: *** [prepare] Error 1
[00:01:36] Makefile:81: recipe for target 'prepare' failed
[00:01:40] Command failed. Attempt 5/5:
[00:01:40] Command failed. Attempt 5/5:
[00:01:40]     Updating crates.io index
[00:01:41] error: the lock file /checkout/Cargo.lock needs to be updated but --locked was passed to prevent this
[00:01:41] Build completed unsuccessfully in 0:00:00
[00:01:41] make: *** [prepare] Error 1
[00:01:41] Makefile:81: recipe for target 'prepare' failed
[00:01:41] The command has failed after 5 attempts.
---
travis_time:end:0ed12b15:start=1543960896617051379,finish=1543960896622972360,duration=5920981
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:017b0d3a
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:009aa5a3
travis_time:start:009aa5a3
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:191a4f50
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[steveklabnik]

okay, locally i am 99% sure this passed (it failed on some extraneous files)

[steveklabnik]

r? @Mark-Simulacrum @rust-lang/release

getting this in today or tomorrow's nightly means I'll be able to link to it from the release blog post.

[pietroalbini]

@bors p=10

[pietroalbini]

@bors r+ p=10

[bors]

📌 Commit 6b0ac49 has been approved by pietroalbini

[pietroalbini]

This is cherry-picked in 1.31.0 stable.

[pietroalbini]

@bors p=20

Moving this ahead of the rollup to make sure it's merged on master ASAP (before the master->beta promotion).

[bors]

⌛ Testing commit 6b0ac49 with merge d8046ed...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: pietroalbini
Pushing d8046ed to master...