This travis environment contains more up-to-date versions of clang and
gcc (namely 7.0.0 and 5.4.0). This allows us to remove all the code used
to get those newer versions in trusty.
Ref: https://docs.travis-ci.com/user/reference/xenial/
Uses none of the optional dependencies. This ensures that polybar can
build without any of the supposedly optional dependencies. This would
have detected the cause of the xrm build failure before it was merged
Before, because of [ -d "$search" ] || search="$(dirname "$search")",
clang-format.sh would search for files to format in the whole repo
(even in the build directory and the submodules)
This now also looks for source files in the tests folder
I have removed the clang-format from clang-tidy.sh because one may want
to run clang-tidy without reformatting
install_xcb_xrm.sh takes advantage of the travis cache but it doesn't
actually install the libraries on the system when it finds that the
compilation has been cached.
