Update PULL_REQUEST_TEMPLATE.md (#616)

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,14 +1,14 @@
-# Before submitting
+## What does this PR do?
+
+Fixes #\<issue_number>
+
+## Before submitting
 
 - [ ] Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
 - [ ] Did you read the [contributor guideline](https://github.com/PyTorchLightning/pytorch-lightning/blob/master/.github/CONTRIBUTING.md), Pull Request section?
 - [ ] Did you make sure to update the docs?
 - [ ] Did you write any new necessary tests?
 
-## What does this PR do?
-
-Fixes # (issue).
-
 ## PR review
 
 Anyone in the community is free to review the PR once the tests have passed.