chore: update pull_request_template.md (#1699)

Author: fedeci

.github/pull_request_template.md

@@ -3,7 +3,7 @@ Add a descriptive title textbox above, e.g.
 feat(validatorName): brief title of what has been done
 -->
 
-{{ briefly describe what you have done in this PR }}
+<!--- briefly describe what you have done in this PR --->
 
 ## Checklist