trying to fix OSX Homebrew installation of gcc4.8

.travis.yml

@@ -19,6 +19,7 @@ script:
   # On OSX, gcc is a wrapper around clang, so use gcc from homebrew
   - if [[ "${TRAVIS_OS_NAME}" == "osx" ]] && [[ "${CC}" == "gcc" ]]; then
        brew install gcc48;
+       brew link --overwrite gcc@4.8;
        export CC=gcc-4.8;
        export CXX=g++-4.8;
     fi