Upgrate travis to cache homebrew dir.

From:
InsightSoftwareConsortium/ITKModuleTemplate#17

Author: phcerdan

.travis.yml

@@ -6,7 +6,7 @@ compiler:
 - gcc
 cache:
   directories:
-  - "$HOME/deps"
+  - "$HOME/Library/Caches/Homebrew"
 script:
 - curl -L https://rawgit.com/InsightSoftwareConsortium/ITKPythonPackage/master/scripts/macpython-download-cache-and-build-module-wheels.sh -O
 - chmod u+x macpython-download-cache-and-build-module-wheels.sh