Revert "Revert "Update APT source for builds on GCE""
Revert "Revert "Update APT source for builds on GCE""

This reverts commit f1ef92af4649980050afa7c7dfd76245ecfb5128.

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