Csslint only evaluate files under '/app/assets'
Revert "Configure numeric log level in production"

This reverts commit cdb4414232dc582016be4ff7f26f90e9ff212afb.
Update version of libyaml used

https://www.ruby-lang.org/en/news/2014/03/29/heap-overflow-in-yaml-uri-escape-parsing-cve-2014-2525/