Use instances of interface for variable definitions.

[idimopoulos]

In PHPStorm, there is a complaint about the $og_roles being an instance of OgRole and not of OgRoleInterface. Fixing very minor documentation entries.

$membership
      ->setOwner($user)
      ->setGroup($collection)
      ->setState($state)
      ->setRoles($og_roles)
      ->save();

[pfrenssen]

Thanks! But it seems this is blocked by some new coding standards violations that are being detected by a new version of phpcs / coder.

This is blocked on #700

[pfrenssen]

Approving and this can be merged without having a passing test suite, since this is a documentation fix which does not affect tests.