setKeysForSaveQuery function returns instance of Builder

Documentation said the setKeysForSaveQuery function returns void but it actually returns the instance of Illuminate\Database\Eloquent\Builder as indicated by the where() function in Illuminate\Database\Query\Builder.

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Merge pull request #670 from driesvints/dv/fix-phpdoc-comments

setKeysForSaveQuery function returns instance of Builder