CLC-4267 - Make sure travis build fails when scss-lint fails

https://jira.ets.berkeley.edu/jira/browse/CLC-4267

Big change was running it instead of "before_install" into "script"
Example of failure at https://travis-ci.org/ets-berkeley-edu/calcentral/jobs/37350486
CLC-4267 - Add vendor to ignored directories
CLC-4267 - Exclude testext & production
Merge pull request #3060 from christianv/CLC-4267

CLC-4267 - Make sure travis build fails when scss-lint fails