Include gcc on mac into PR matrix

There was an error that slipped through and only showed up on PR merge (https://travis-ci.org/google/googletest/jobs/364304396/config ) , we dont want that again

.travis.yml

@@ -43,7 +43,6 @@ matrix:
     - os: osx
       compiler: gcc
       env: BUILD_TYPE=Release VERBOSE=1 CXX_FLAGS=-std=c++11
-      if: type != pull_request
     - os: osx
       compiler: clang
       env: BUILD_TYPE=Debug VERBOSE=1