Fix javadoc todo link

go/todont

Author: daymxn

buildSrc/src/main/java/com/google/firebase/gradle/plugins/JavadocPlugin.java

@@ -117,7 +117,7 @@ private static void applyDoclava(Project project) {
                 // This comes with the risks of Timestamp's javadoc and binary releases having
                 // disconnected timelines.
                 // Given the repeated tedium in dealing with javadoc, this risk seems worth taking
-                // b/243534168
+                // TODO(b/243534168): Move Timestamp class to firebase-common
                 if ("firebase-common".equals(project.getName())) {
                   Project firestoreProject = project.findProject(":firebase-firestore");
                   javadoc.setSource(