Finish TravisCI builds more quickly

Builds that are allowed to fail [shouldn't have to
finish](https://docs.travis-ci.com/user/customizing-the-build/#Fast-Finishing)
for the build to be finished.

Author: xiongtx

.travis.yml

@@ -14,6 +14,7 @@ env:
 matrix:
   allow_failures:
     - env: EMACS_BINARY=emacs-git-snapshot-travis
+  fast_finish: true
 before_script:
   - curl -fsSkL https://gist.github.com/rejeep/ebcd57c3af83b049833b/raw > x.sh && source ./x.sh
   - evm install $EMACS_BINARY --use --skip