GH: Update pull-request template

100% code coverage is a lie, as there are parts that are being ignored.
All we want to achive is not regressing coverage. While slowly working
towards increasing it.

Author: slyon

.github/pull_request_template.md

@@ -5,7 +5,7 @@
 ## Checklist
 
 - [ ] Runs `make check` successfully.
-- [ ] Retains 100% code coverage (`make check-coverage`).
+- [ ] Retains code coverage (`make check-coverage`).
 - [ ] New/changed keys in YAML format are documented.
 - [ ] \(Optional\) Adds example YAML for new feature.
 - [ ] \(Optional\) Closes an open bug in Launchpad.