Travis/macOS: Don't install ccache in the test phase.

This should save a minute or so.

.travis.yml

@@ -93,7 +93,7 @@ before_install:
   - if [ -f $BUILD_LIBS/config.cache.libev ]; then cp $BUILD_LIBS/config.cache.libev deps/libev/config.cache ; fi
   - if [ -f $BUILD_LIBS/config.cache.libuv ]; then cp $BUILD_LIBS/config.cache.libuv deps/libuv/config.cache ; fi
   - |
-    if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then
+    if [[ "$TRAVIS_OS_NAME" == "osx" && "$TRAVIS_BUILD_STAGE_NAME" != "Test" ]]; then
       brew install ccache
       export PATH="/usr/local/opt/ccache/libexec:$PATH"
       export CFLAGS="$CFLAGS -Wno-parentheses-equality"