travis: increase xcode/clang version.
travis: increase xcode/clang version.

johne53/MB3Liblo,johne53/MB3Liblo,johne53/MB3Liblo,radarsat1/liblo,tuscland/liblo,radarsat1/liblo,tuscland/liblo,johne53/MB3Liblo,tuscland/liblo,radarsat1/liblo