set insecure_ssl to webhook config

Without insecure_ssl, sites which use https with self-hosted cert can't receive
pull_request web hook.
the option is also set to "1" when adding webhook URL via GitHub Web UI.
Merge pull request #78 from k2nr/insecure_ssl

set insecure_ssl to webhook config
when comment contains trigger phrase, start build of the PR and buidld onlyTriggerPhrase jobs only when trigger phrase is really submited
[maven-release-plugin] prepare release ghprb-1.9
[maven-release-plugin] prepare for next development iteration