increase travis max runtime to 30min

this is described here: https://docs.travis-ci.com/user/common-build-problems/#My-builds-are-timing-out

.travis.yml

@@ -11,7 +11,7 @@ before_install:
   - gem --version
   - bundle -v
 script:
-  - 'bundle exec rake $CHECK'
+  - 'travis_wait 30 bundle exec rake $CHECK'
 matrix:
   fast_finish: true
   include: