* Allow nightly Yarn builds to be used
Fixes:
```
C:\src\babel (fix-it-fix-it-fix-it-fix-it) (babel)
λ yarn
yarn install v1.0.0-20170811.1240
[1/5] Validating package.json...
error babel@: The engine "yarn" is incompatible with this module. Expected version ">=0.27.5".
error Found incompatible module
info Visit https://yarnpkg.com/en/docs/cli/install for documentation about this command.
```
* Use Yarn 0.28.4 to fix build
* Move babel-standalone into main Babel repo
* Don't try to gather coverage data for babel-standalone test
* Fix JSX test
* Always use npm v4 on Travis
* Include pull request number as part of version number
* Cherry-picking 5721b2e43e
Remove deprecated packages to prevent Babel v6 files from being pulled in
* Use RootMostResolvePlugin to dedupe packages
* Avoid destructuring so the build works on archaic Node.js versions
* - Fix version number
- Remove Babili packages (they should be in separate babili-standalone)
- Remove deprecated syntax-class-constructor-call
* - Remove more Babili packages
- Remove `babel-plugin-inline-replace-variables` for now as it pulls in Babel 6 stuff
* Actually remove reference to babel-plugin-undeclared-variables-check
* Add Babylon to root package.json so we hoist the right version. This fixes the tests.
* update lerna and lerna-changelog
* Lerna: enable yarn, yarn workspaces [skip ci]
* use older version of Babel since it matches on semver (cannot be the same version)
* install yarn version
* revert node engine change
* update flow
* circle ci on 8
* update lock
* Switch to nyc, babel-plugin-istanbul & codecov-node for code coverage
This setup (very much like Babylon's) let us trace code coverage back to the `src/` directories of packages.
* Exclude package tests from coverage report
* fix: upgrade to version of nyc that tweaks a couple more things for babel
* fix: remove comment based on @hzoo's review
