How can i setup github pull requests to generate a build?

i want to add specific behavior for pull requests for that i need the pull request itself to generate a new build, and it doesn’t seem to do that (on travis for example it does, configurable by me).
The point is that i might have a release branch ready for release and deploy code that changes and commits the app version(increase revision, naming the version name like the branch name) merges the release branch pull request (if exists) to master, delete the release branch, tag the master with the name of the branch.
Right now for all this to happen i need to open a pull request AND do some silly commit, it would be much easier if i could just have the pull request to generate the build.
(again on travis it’s possible)


Any other idea except having travis working on the same repo and instead of building asking circle to rebuild the branch that has the pull request on it using circleci api ?