automate brew update through Travis

@Juice10 added a great feature where `wskdeploy` CLI can be downloaded through `brew`. We need an automation to update `brew` so that whenever `wskdeploy` release is created, a new binary is available through `brew install`.

@Juice10 can you please take care of this?

Start by tracing how wskdeploy releases are created and how the existing brew installation path is maintained, then inspect the Travis automation involved in releases. Done means a new wskdeploy release automatically makes its binary available through brew install; the issue names no files or tests to run.

Written by the indexing model from the issue text.