Fixing DocBlock for Model.php

Fixing a small typo and adding `@var array` to DocBlock for new appends functionality.
Merge pull request #2115 from jenssegers/4.0

Fixing DocBlock for Model.php
Cleaning up some tech debt in the Eloquent builder and relationship management.
Return the array from array_set.
Fix typo in doc block.
Fix spacing in doc block.
Get default connection name on null reconnect.
Added new preg_replace_array helper.
Pass replacements by reference and rename function.