447: Sponsoring should only require committer status

Reviewed-by: jvernee

bots/pr/src/main/java/org/openjdk/skara/bots/pr/SponsorCommand.java

@@ -40,7 +40,7 @@ public void handle(PullRequestBot bot, PullRequest pr, CensusInstance censusInst
             reply.println("This change does not need sponsoring - the author is allowed to integrate it.");
             return;
         }
-        if (!censusInstance.isReviewer(command.user())) {
+        if (!censusInstance.isCommitter(command.user())) {
             reply.println("Only [Committers](https://openjdk.java.net/bylaws#committer) are allowed to sponsor changes.");
             return;
         }