Fixes jclouds-representations pom artifactId to use correct spelling

This PR fixes a simple typo in the jclouds-representations project poms.

Please refer to the [Maven Central Repository](http://search.maven.org/#artifactdetails%7Corg.apache.jclouds.labs%7Cjclouds-represetations%7C1.7.2%7Cpom)

The incorrect spelling of the artifactId has been present since [1.6.1-incubating](http://search.maven.org/#search%7Cgav%7C1%7Cg%3A%22org.apache.jclouds.labs%22%20AND%20a%3A%22jclouds-represetations%22)