PHPCS 3.6.2 added a sniff for a PSR-12 rule which was previously not strictly checked: "No blank line after the opening brace of a class".
This fixes the newly flagged issues.
Minor test tweaks:
* Add `@coversNothing` tag.
* Rename the first test (add a number).
* Use `@link` instead of `@see` for links.
* Minor comment punctuation.