travis: Set deploy.skip_cleanup to true.
travis: Set deploy.skip_cleanup to true.

As described in https://docs.travis-ci.com/user/deployment/releases/

Hopefully this will get deployment to github releases working again.
Though I don't quite understand how it ever worked before without it,
nor why isn't this the default already.

jrfonseca/drmingw,jrfonseca/drmingw,jrfonseca/drmingw,jrfonseca/drmingw