Upgrate travis to cache homebrew dir.
Upgrate travis to cache homebrew dir.

From:
https://github.com/InsightSoftwareConsortium/ITKModuleTemplate/pull/17

jhlegarreta/ITKIsotropicWavelets,phcerdan/ITKIsotropicWavelets,phcerdan/ITKIsotropicWavelets,jhlegarreta/ITKIsotropicWavelets