fix pre-version enforcement

when using a pre-release version (for example an RC), the plugin should validate against the next release version:
http://semver.org/
"A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version"

The main change is:
```current.toReleaseVersion().compareTo(inferredVersion) >= 0;```

that way when publishing 1.6.0-rc2 I don't get a message that it should be at least 1.6.0