Patch (#44)

* Add Maven goal `-Drun.port` argument support

Author: hearts-thaw

invoker/function-maven-plugin/src/main/java/com/google/cloud/functions/plugin/RunFunction.java

@@ -72,6 +72,9 @@ public void execute() throws MojoExecutionException {
     if (functionTarget != null) {
       args.addAll(Arrays.asList("--target", functionTarget));
     }
+    if (port != null) {
+      args.addAll(Arrays.asList("--port", String.valueOf(port)));
+    }
     try {
       getLog().info("Calling Invoker with " + args);
       Invoker.main(args.toArray(new String[0]));