Fix integration build

Homebrew started getting stuck with gcc-6
Temporarily switch to gcc-5
diff --git a/.travis.yml b/.travis.yml
index 5bccc6d..005a1f1 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -138,10 +138,10 @@
     ## all since we already test all these versions of GCC on Linux.
     ## We'll just test 4.4 and the most recent version.
     ###
-    - os: osx
-      env: BUILD_SYSTEM=cmake C_COMPILER=gcc-6 CXX_COMPILER=g++-6
-    # - os: osx
-    #   env: BUILD_SYSTEM=cmake C_COMPILER=gcc-5 CXX_COMPILER=g++-5
+    #- os: osx
+    #  env: BUILD_SYSTEM=cmake C_COMPILER=gcc-6 CXX_COMPILER=g++-6
+     - os: osx
+       env: BUILD_SYSTEM=cmake C_COMPILER=gcc-5 CXX_COMPILER=g++-5
     # - os: osx
     #   env: BUILD_SYSTEM=cmake C_COMPILER=gcc-4.9 CXX_COMPILER=g++-4.9
     # - os: osx