[bugfix] Database\Query\Builder::groupBy() now accepts arrays as arguments

I'm not actually sure whether this is a bug or a new feature. I am presuming this is a bug-fix only because the comment above the function definition for Database\Query\Builder::groupBy() says that the $columns parameter is "dynamic". I'm presuming that means it is of dynamic individual argument type (assuming array or string) and dynamic length of arguments. See [this stack overflow post for a full description of the issue] (http://stackoverflow.com/questions/23185432/group-by-multiple-columns-in-laravel/24415397#24415397) for more detail.

In any case, if Database\Query\Builder::groupBy() could accept arrays as is proposed in this "fix", it would resolve some confusion. As it is now, tracing the bug that results when trying to pass an array to groupBy() is extremely difficult.

The alternate solution would be to change the comment above groupBy() to more accurately state that the $columns parameter is only "dynamic" in the sense that it can accept N number of string arguments.