Try adding osx to travis

.travis.yml

@@ -93,7 +93,7 @@ matrix:
 before_script:
   - if [ -n "$GCC_VERSION" ]; then export CXX="g++-${GCC_VERSION}" CC="gcc-${GCC_VERSION}"; fi
   - if [ -n "$CLANG_VERSION" ]; then export CXX="clang++-${CLANG_VERSION}" CC="clang-${CLANG_VERSION}"; fi
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; export CXX="clang++" CC="clang"; fi
+  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then export CXX="clang++" CC="clang"; fi
   - which $CXX
   - which $CC
   - which valgrind