Merge pull request #224 from illwieckz/travis

fix travis on macos (brew update)

Author: illwieckz

.travis.yml

@@ -35,6 +35,7 @@ install:
         liblua5.2-dev ninja-build;
     fi
   - if [ "$TRAVIS_OS_NAME" == "osx" ]; then
+      brew update;
       brew install ccache ninja;
     fi
   - |