Remove line breaks from pull request template

Author: Cito

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,15 +1,9 @@
 Thank you for contributing to GraphQL-core!
 
-If your pull-request is non-trivial, adds a feature or contains a non-breaking change,
-then please, first open an issue to discuss the proposed changes and add a link to it.
+If your pull-request is non-trivial, adds a feature or contains a non-breaking change, then please, first open an issue to discuss the proposed changes and add a link to that issue.
 
-GraphQL-core tries very hard to stay within the scope of being just a Python port
-of [GraphQL.js](https://github.com/graphql/graphql-js).
+GraphQL-core tries very hard to stay within the scope of being just a Python port of [GraphQL.js](https://github.com/graphql/graphql-js).
 
-Any additional feature  or incompatible change will be only accepted in rare cases
-and require compelling reasons, because they aggravate maintenance and synchronization
-with the developments in the upstream project. So please discuss such changes upfront
-in an issue before sending a PR. Maybe there are other ways to solve the problem.
+Any additional feature or incompatible change will be only accepted in rare cases and requires a compelling reason, because they aggravate maintenance and synchronization with the developments in the upstream project. So please discuss such changes upfront in an issue before sending a PR. Maybe there are other ways to solve the problem.
 
-If possible, also add unit tests, or provide runnable example code as part of the
-accompanying issue, from which unit tests can be derived.
+If possible, also add unit tests, or provide runnable example code as part of the accompanying issue, from which unit tests can be derived.