chore(ci): finish different matrixes in fast finish mode (#1138)

Travis CI runs the optional tasks in "waiting" mode, which means that the whole build is only ready once the optional tasks are also ready.
The Travis Fast Finish mode will mark the build as finished, once all "required" tasks have finished (https://blog.travis-ci.com/2013-11-27-fast-finishing-builds/)

Author: devversion

.travis.yml

@@ -37,6 +37,7 @@ env:
     - MODE=browserstack_optional
 
 matrix:
+  fast_finish: true
   allow_failures:
   - env: "MODE=saucelabs_optional"
   - env: "MODE=browserstack_optional"