Update: Upgrade Acorn to support ES2017 (fixes #287)

[xjamundx]

This PR adds support for ecmaVersion: 8 to espree by using the latest acorn.

The main requested new feature here is support for async and await.

I copied all of the test cases from the acorn test suite here (there are piles of them):
https://github.com/ternjs/acorn/blob/master/test/tests-asyncawait.js

Still needs rebasing, etc.

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[nzakas]

Can you add some tests for trailing commas in function arguments too?

function foo(a, b,) {}

var foo = function(a, b,) {};

var foo = (a, b,) => {};

foo(a, b,);

[xjamundx]

Certainly!

[xjamundx]

Added comma-dangle tests

[xjamundx]

Hold on, some issues with the tests. 1 sec.

[xjamundx]

K tests are in. Turns out your tests should default to script for the sourceType isntead of module. Should have realized.

[xjamundx]

Oh and I need to fix my github author. Used my paypal account...

[xjamundx]

Just squashed it into your orgiinal commit if that's alright.

[mysticatea]

Wow, amazing, near 20K lines 😮

[xjamundx]

Lol @mysticatea it's just the generated tests. New code is like 10 lines.

[nzakas]

LGTM. Awesome stuff!