Update HHVM on Precise
Update HHVM on Precise

To get HHVM 3.6, the last version supported on Precise.

https://github.com/facebook/hhvm/wiki/Prebuilt-Packages-on-Ubuntu-12.04

luoqii/travis-build,kevmoo/travis-build,craigcitro/travis-build,JuliaCI/travis-build,luoqii/travis-build,tmccombs/travis-build,craigcitro/travis-build,akoeplinger/travis-build,kevmoo/travis-build,andyli/travis-build,andyli/travis-build,dirk/travis-build,dirk/travis-build,tmccombs/travis-build,JuliaCI/travis-build,gavioto/travis-build,jhass/travis-build,akoeplinger/travis-build,jhass/travis-build,gavioto/travis-build