Travis: work around unfriendly defaults on MacOS
Travis: work around unfriendly defaults on MacOS

See travis-ci/travis-ci#8826

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

VcDevel/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc