GenerateGradleRb task(s) don't resolve a custom configuration's dependencies

[tommysullivan]

tasks.jrubyGenerateGradleRb {
    configuration configurations.rspec

}
import com.github.jrubygradle.GenerateGradleRb
task testCustomConfig(type: GenerateGradleRb) {
    configuration configurations.rspec
}

Neither of the tasks above end up installing the gems inside of the rspec configuration directory, but instead seem to pull in whatever gems are in the jrubyExec configuration.

The tasks do however express a task dependency on jrubyPrepareGems however.

[rtyler]

Related to #237