Update pull_request_template.md

.github/pull_request_template.md

@@ -1,8 +1,8 @@
 <!--
 Thank you for submitting a pull request!
 
-Here's a checklist you might find useful.
-* [ ] There is an associated issue that is labeled 'Bug' or 'help wanted'
+Please verify that:
+* [ ] There is an associated issue in the `Backlog` milestone (**required**)
 * [ ] Code is up-to-date with the `master` branch
 * [ ] You've successfully run `gulp runtests` locally
 * [ ] There are new or updated unit tests validating the change
@@ -12,4 +12,3 @@ Refer to CONTRIBUTING.MD for more details.
 -->
 
 Fixes #
-