Fix minification report. Use default Ruby.

Fixed the minification report on Travis CI to account for the relocation
of the `timezone.js` source file.

The default Ruby at Travis CI is now 1.9.3p286 which supports the `%::z`
format specifier, so we no longer need to install a Ruby with `apt-get`
from a Personal Package Archive.
Merge branch `directory` into `travis-ci`.