Travis CI: re-enable MW 1.15 tests
Travis CI: re-enable MW 1.15 tests

Travis finally working. Tests were passing on MW master after adding
a "composer selfupdate" to "before_script.sh".

DanweDE/mediawiki-ext-UserBitcoinAddresses,DanweDE/mediawiki-ext-UserBitcoinAddresses,DanweDE/mediawiki-ext-UserBitcoinAddresses