Allow [ci skip] to work for non-pull request changes

the README for version 0.1.1 of https://plugins.jenkins.io/bitbucket-scm-trait-commit-skip indicates, in the Description, that "The filtering is only performed at change requests events, so push events to non-pull requests will be always run."

it would be totally amazing and make my day if this functionality applied equally to non-pull request changes (we never build pull requests).

i assigned it to you, javier, just to make sure you'd see it. please feel free to detach yourself.