Revert "Try https://blog.travis-ci.com/2017-12-01-new-update-schedule-for-linux-build-images."
Revert "Try https://blog.travis-ci.com/2017-12-01-new-update-schedule-for-linux-build-images."

This reverts commit 9cc7222996dc189a816ddad293ad7e1ff0829fe4.

anarkiwi/faucet,gizmoguy/faucet,shivarammysore/faucet,REANNZ/faucet,trungdtbk/faucet,trentindav/faucet,gizmoguy/faucet,faucetsdn/faucet,mwutzke/faucet,wackerly/faucet,shivarammysore/faucet,faucetsdn/faucet,trentindav/faucet,anarkiwi/faucet,trungdtbk/faucet,REANNZ/faucet,wackerly/faucet,mwutzke/faucet