i#3194 doc-deploy: Push to master branch
i#3194 doc-deploy: Push to master branch

Turns out the default is for Travis to push to the "gh-pages" branch
which we are not using.  We specify the master branch here.

Issue: #3194

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio