npm.commands.version(newversion, callback)
Run this in a package directory to bump the version and write the new data back to the package.json file.
If run in a git repo, it will also create a version commit and tag, and fail if the repo is not clean.
Like all other commands, this function takes a string array as its first parameter. The difference, however, is this function will fail if it does not have exactly one element. The only element should be a version number.