Prevent Travis from double-building PRs
Prevent Travis from double-building PRs

This magic incantation tells Travis to build
pushes only against master. Practically, that
includes merge commits. PRs count as a separate
build, so this means that:

  * PRs will build once
  * Master will build once they merge

gocardless/statesman,gocardless/statesman,timothyp/statesman,timothyp/statesman