Do not always bump but just copy version from package.json

Not sure if it's not completely pointless to offer a 'no-bump' option in a grunt-bump-pom task, but I liked the backup and version check (and the optional possibility to bump when needed)

I use it to manage my version inside package.json only, and start a 'maven clean deploy' to update the artifact to nexus or install it on my local repo, which should reflect the built version by grunt.

So I need to take over package.json version without bumping it again.