Mark the storm extension as incubating for now

Given the troubles with jruby.defaultVersion in the code plugins, I'm not sure
this is a great pattern

.gitignore

@@ -1,8 +1,8 @@
 .gradle
 build/
+.idea/
 
 # Ignore Gradle GUI config
 gradle-app.setting
 *.sw*
-.idea/
 *.iml

src/main/groovy/com/github/jrubygradle/storm/JRubyStormExtension.groovy

@@ -1,13 +1,16 @@
 package com.github.jrubygradle.storm
 
+import org.gradle.api.Incubating
 
 /**
- *
+ * Extension to provide the `project.storm` DSL into a Gradle project
  */
 class JRubyStormExtension {
+    @Incubating
     /** Default version of Storm supported and included */
     String defaultVersion = '0.9.2-incubating'
 
+    @Incubating
     /** Default version of redstorm to use */
     String defaultRedstormVersion = '0.7.2'