Refactor Travis CI

[CruzMolina]

This PR refactors CI tests to only install external dependencies for relevant jobs. Also ensures only relevant tests for each job are ran (i.e. geth tests in truffle-contract now skipped in non-geth jobs).

Specific streamlined dependencies:
docker pull for solc & geth, apt-get for jq & snapd, & snap install vyper.

Saves us ~4-5 min for the build.
Resolves #1336.

Also includes updated yarn.lock left out from #1930 .

[coveralls]

Coverage decreased (-0.3%) to 69.37% when pulling 88b16c0 on travis-refactor into 8abe024 on develop.

[cgewecke]

@CruzMolina Sorry for looking over your shoulder here but possibly this change should be revisited:

geth tests in truffle-contract now skipped in non-geth jobs

Ideally all the tests should pass ganache and but only a subset of them will pass on geth, hence the geth tag.

This is relevant wrt #1852 (upgrade web3) because it looks like many of the relevant tests are now hidden in an allowed failure on CI? Forgive me if I've misunderstood this.

[CruzMolina]

Thanks for checking in on geth integration @cgewecke.

I think it's probably time to move the geth job out of it's allowed failure state.