Fix typo in pull request template

PULL_REQUEST_TEMPLATE.md

@@ -2,5 +2,5 @@ Thanks for contributing to react-virtualized!
 
 Here is a short checklist of additional things to keep in mind before submitting:
 * Please make sure your pull request description makes it very clear what you're trying to accomplish. If it's a bug fix, please also provide a failing test case (if possible). In either case, please add additional unit test coverage for your changes. :)
-* Run tests locally (`npm test`) to ensure that your change did not break linting of functionality.
+* Run tests locally (`npm test`) to ensure that your change did not break linting or functionality.
 * Be sure you have notifications setup so that you'll see my code review responses. (I may ask you to make some adjustments before merging.)