Try compile with gcc-6 on macOS X

Author: forthy42

.travis.yml

@@ -10,6 +10,6 @@ sudo: true
 before_install: ./install-deps.sh
 script:
   - ./autogen.sh
-  - if [ "${TRAVIS_OS_NAME}" = osx ]; then export CC=gcc-6.2; fi
+  - if [ "${TRAVIS_OS_NAME}" = osx ]; then export CC=gcc-6; fi
   - ./configure --enable-lib CC="$CC $M32"
   - make