Cache brew dir on travis

Author: Pan

.travis.yml

@@ -3,6 +3,7 @@ cache:
   - pip
   - directories:
       - "$HOME/.pyenv"
+      - "$HOME/Library/Caches/Homebrew"
 notifications:
   email: false
 sudo: required
@@ -47,8 +48,11 @@ jobs:
       osx_image: xcode9.2
       env:
         - SYSTEM_LIBSSH2: 1
+      before_cache:
+        - brew cleanup
       before_install:
         - brew update
+        - brew install ccache
         - brew outdated openssl || travis_wait brew upgrade openssl || echo "y"
         - brew link --overwrite python@2 || brew install python@2 || brew link --overwrite python@2
         - which python2