Updated mediawiki/extensions
Project: mediawiki/extensions/Wikibase  75799f12f6a2d26855d8ee7a58ed41fd794c5196

Tweak TravisCI build: get deps via git rather than tarball

This is to sidestep flakyness in the GitHub tarball API

Change-Id: I45eb7b5abdddbae2142de319814b32b5120a8d7e