add pr into travis

.travis.yml

@@ -20,6 +20,11 @@ addons:
       - python-wheel
       - clang-format-3.8
       - ccache
+
+script:
+   - 'if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then bash ./travis/run_on_pull_requests; fi'
+   - 'if [ "$TRAVIS_PULL_REQUEST" = "false" ]; then bash ./travis/run_on_non_pull_requests; fi'
+
 notifications:
   email:
     on_success: change