Add Prettier (#3011)

Consistent code formatting!
(it fixed a few minor bugs too)

.github/CONTRIBUTING.md

@@ -12,7 +12,6 @@ the developers managing and developing this open source project. In return,
 they should reciprocate that respect in addressing your issue or assessing
 patches and features.
 
-
 ## Using the issue tracker
 
 The [issue tracker](https://github.com/h5bp/html5-boilerplate/issues) is
@@ -20,19 +19,19 @@ the preferred channel for [bug reports](#bugs), [features requests](#features)
 and [submitting pull requests](#pull-requests), but please respect the following
 restrictions:
 
-* Please **do not** use the issue tracker for personal support requests (use
+- Please **do not** use the issue tracker for personal support requests (use
   [Stack Overflow](https://stackoverflow.com/questions/tagged/html5boilerplate)).
 
-* Please **do not** derail or troll issues. Keep the discussion on topic and
+- Please **do not** derail or troll issues. Keep the discussion on topic and
   respect the opinions of others.
 
-* Please **do not** open issues or pull requests regarding the code in
+- Please **do not** open issues or pull requests regarding the code in
   [`.htaccess`](https://github.com/h5bp/server-configs-apache),
   [`Normalize.css`](https://github.com/necolas/normalize.css) (open them in
   their respective repositories).
 
-
 <a name="bugs"></a>
+
 ## Bug reports
 
 A bug is a _demonstrable problem_ that is caused by the code in the repository.
@@ -73,17 +72,17 @@ Example:
 > causing the bug, and potential solutions (and your opinions on their
 > merits).
 
-
 <a name="features"></a>
+
 ## Feature requests
 
 Feature requests are welcome. But take a moment to find out whether your idea
-fits with the scope and aims of the project. It's up to *you* to make a strong
+fits with the scope and aims of the project. It's up to _you_ to make a strong
 case to convince the project's developers of the merits of this feature. Please
 provide as much detail and context as possible.
 
-
 <a name="pull-requests"></a>
+
 ## Pull requests
 
 Good pull requests - patches, improvements, new features - are a fantastic
@@ -146,7 +145,7 @@ included in the project:
    ```
 
 7. [Open a Pull Request](https://help.github.com/articles/using-pull-requests/)
-    with a clear title and description.
+   with a clear title and description.
 
 **IMPORTANT**: By submitting a patch, you agree to allow the project
 owners to license your work under the terms of the [MIT License](LICENSE.txt).