Remove range_key query restriction

The [doc](http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_Query.html) says, that range_key criteria is optional:

> For a query on a table, you can only have conditions on the table primary key attributes. You must specify the hash key attribute name and value as an EQ condition. You can optionally specify a second condition, referring to the range key attribute.

This is probably left from a older protocol version. What do you think?