Makes it possible to pass in basic request parameters as arrays

For example it wasn't possible to send invite requests as follows:

```ruby
@graph.put_connections(1234567, "invited", :users => [1,2,3,4,5])
```

Instead in order to work with the API you'd need to do something
similar to:

```ruby
user_ids = [1,2,3,4,5].join(',')
@graph.put_connections(1234567, "invited", :users => user_ids)
```

This fixes that.