jenkins: only trigger on nodejs/node PRs
jenkins: only trigger on nodejs/node PRs

PR-URL: https://github.com/nodejs/github-bot/pull/184
Reviewed-By: Phillip Johnsen <470e1382ee18f73c6e6136d311417869a87d7cf6@gmail.com>
Reviewed-By: Joyee Cheung <c24c8f580289b8360adc3fe49d66727180fe8aa3@gmail.com>
phillipj/github-bot,nodejs/github-bot