Update query-builder.rst

Added some type hinting to the example so that it's easier to understand what the params actually are. Plus it gives users the ability to easily track down available methods on $results
Change ResultSetInterface to ResultSet

Made the change to prevent people hitting a PHP warning
Fixed the namespace

Updated the namespace to reference the correct class.
Merge pull request #1902 from davidyell/patch-10

Update query-builder.rst