Temporarily disable OS X build on Travis-CI.
Temporarily disable OS X build on Travis-CI.

This is because we updated to Qt 5.4 and brew doesn’t yet have it.

mirams/opencor,mirams/opencor,mirams/opencor,mirams/opencor,Fairly/opencor,Fairly/opencor,mirams/opencor,Fairly/opencor,Fairly/opencor,Fairly/opencor