Add Gradle version check to prevent usage of deprecated settingsFile property

Author: IRus

src/main/groovy/net/researchgate/release/ReleasePlugin.groovy

@@ -31,6 +31,7 @@ import org.gradle.api.Task
 import org.gradle.api.plugins.BasePlugin
 import org.gradle.api.tasks.GradleBuild
 import org.gradle.api.tasks.TaskState
+import org.gradle.util.GradleVersion
 
 class ReleasePlugin extends PluginHelper implements Plugin<Project> {