Steps to release

This outlines the maintainers steps to release the Jenkins Slack plugin. Follow the Jenkins documentation for making a new release.

Configure your credentials in ~/.m2/settings.xml. (outlined in making a new release doc)
Create a new issue to track the release and give it the label maintainer communication.
Create a release branch. git checkout origin/master -b prepare_release
Update the release notes in CHANGELOG.md.
Open a pull request from prepare_release branch to master branch. Merge it.
Fetch the latest master.
Clean the workspace git clean -xfd.

Execute the release plugin.

mvn org.apache.maven.plugins:maven-release-plugin:2.5:prepare org.apache.maven.plugins:maven-release-plugin:2.5:perform

Wait for the plugin to be released into the Jenkins Update Center.
Successfully perform an upgrade from the last stable plugin release to the current release.

I pin which version of the release plugin to use because of the working around common issues section of the release document.