Use ccache on OSX

.travis.yml

@@ -76,18 +76,17 @@ before_install:
     else
       brew update
       brew tap homebrew/gui
-      brew install python libpng  ffmpeg imagemagick mplayer
+      brew install python libpng  ffmpeg imagemagick mplayer ccache
       # We could install ghostscript and inkscape here to test svg and pdf
       # but this makes the test time really long.
       # brew install ghostscript inkscape
+      export PATH=/usr/local/opt/ccache/libexec:$PATH
     fi
 
 install:
   - |
     # Setup environment
-    if [[ $TRAVIS_OS_NAME != 'osx' ]]; then
-      ccache -s
-    fi
+    ccache -s
     # Upgrade pip and setuptools and wheel to get as clean an install as possible
     pip install --upgrade pip
     pip install --upgrade wheel