Update PULL_REQUEST_TEMPLATE.md

Author: ecordell

.github/PULL_REQUEST_TEMPLATE.md

@@ -12,12 +12,12 @@ Note: Make sure your branch is rebased to the latest upstream master.
 **Motivation for the change:**
 
 **Reviewer Checklist**
-[] Implementation matches the proposed design, or proposal is updated to match implementation
-[] Sufficient unit test coverage 
-[] Sufficient end-to-end test coverage
-[] docs updated or added to `/docs` 
-[] commit messages sensible and descriptive
-[] if implementation differs from proposal, proposal is updated to reflect the changes
+- [ ] Implementation matches the proposed design, or proposal is updated to match implementation
+- [ ] Sufficient unit test coverage 
+- [ ] Sufficient end-to-end test coverage
+- [ ] docs updated or added to `/docs` 
+- [ ] commit messages sensible and descriptive
+- [ ] if implementation differs from proposal, proposal is updated to reflect the changes
 
 
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