Invalid config key in docs

There is invalid configuration key ```grails.plugins.karman``` instead of correct ```grails.plugin.karman``` in [published documentation](http://bertramdev.github.io/karman/guide/configuration.html) despite it is correct in source: [configuration.gdoc#L4](https://github.com/bertramdev/karman-core/blob/master/karman-grails/src/docs/guide/configuration.gdoc#L4)