Properly set up GCC on OS X

.travis.yml

@@ -20,9 +20,12 @@ matrix:
         homebrew:
           packages:
             - astyle
-            - gcc@8
+            - gcc
       before_install:
         - pip3 install -r requirements.txt
+        - export PATH="/usr/local/bin:$PATH"
+        - ln -s /usr/local/Cellar/gcc/8.3.0/bin/gcc-8 /usr/local/bin/gcc
+        - ln -s /usr/local/Cellar/gcc/8.3.0/bin/cpp-8 /usr/local/bin/cpp
         - gcc --version
       script:
         - "cd test && python3 -m nose --rednose --verbose"