Revert "Invoke `yarn` with `--frozen-lockfile`"
Revert "Invoke `yarn` with `--frozen-lockfile`"

andyli/travis-build,JuliaCI/travis-build,craigcitro/travis-build,kevmoo/travis-build,andyli/travis-build,kevmoo/travis-build,craigcitro/travis-build,JuliaCI/travis-build