three markdown files: Fixed spaces

_faq/gsoc-requirements.md --> Trailing whitespaces
_faq/is-mentor-necessary.md --> Trailing whitespaces
_projects/extend-linter-integration.md --> Tabs used instead of spaces

Closes coala#529

_faq/gsoc-requirements.md

@@ -4,5 +4,5 @@ question: "What are the requirements to be accepted for GSoC?"
 Other than the [requirements from Google](https://developers.google.com/open-source/gsoc/faq#what_are_the_eligibility_requirements_for_participation) you will have to meet the following:
 
 * You have completed the [coala Newcomers guide](https://coala.io/newcomer)
-* You have a submission to [our usability survey](https://coala.io/usability) so we know that
-    you know how to *use coala*.
+* You have a submission to [our usability survey](https://coala.io/usability)
+    so we know that you know how to *use coala*.