dev-plugins.txt: Fix example implementation of SubmitRule

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I980d2a558e04c56a53e801b1cb609a76deb738e6

Documentation/dev-plugins.txt

@@ -2678,7 +2678,7 @@ public class MyPluginRules implements SubmitRule {
     // Implement your submitability logic here
 
     // Assuming we want to prevent this change from being submitted:
-    SubmitRecord record;
+    SubmitRecord record = new SubmitRecord();
     record.status = Status.NOT_READY;
     return record;
   }