chore(travis): update travis script, add trigger saucelabs karma test

relates to ReactiveX#998

.travis.yml

@@ -10,6 +10,10 @@ addons:
     packages:
     - gcc-4.8
     - g++-4.8
+    sauce_connect:
+      # Update SAUCE_USERNAME / SAUCE_ACCESS_KEY in travis if necessary
+      # https://docs.travis-ci.com/user/environment-variables/#Defining-Variables-in-Repository-Settings
+      sauce_connect: true
 
 cache:
   directories:
@@ -25,7 +29,10 @@ install:
   - npm install && npm run lint
 
 script:
-  - npm test && node ./node_modules/markdown-doctest/bin/cmd.js && npm run cover && npm run check_circular_dependencies
+  - npm test && node ./node_modules/markdown-doctest/bin/cmd.js
+  - npm run check_circular_dependencies
+  - npm run cover
+  - cat ./coverage/coverage-remapped.lcov | ./node_modules/coveralls/bin/coveralls.js
 
-after_script:
-  - cat ./coverage/coverage-remapped.lcov  | ./node_modules/coveralls/bin/coveralls.js
+after_success:
+  - '[ "${TRAVIS_PULL_REQUEST}" = "false" ] && [ -n "${SAUCE_ACCESS_KEY}" ] && npm run test_karma || false'