Merge branch 'master' of https://github.com/webpack/webpack into jest

# Conflicts:
#	.eslintrc.js
#	package.json
#	test/BenchmarkTestCases.benchmark.js
#	test/ConfigTestCases.test.js
#	test/NodeWatchFileSystem.unittest.js
#	test/TestCases.test.js
#	test/WatcherEvents.test.js
#	test/cases/parsing/extract-require/index.js
#	test/configCases/parsing/harmony-this/index.js
#	test/statsCases/async-commons-chunk/expected.txt
#	yarn.lock