Add 'query' to available attribute writers so it can be set with 'new'

At the the moment, ```HTTPI::Request.new``` ignores ```query``` as a parameter.

```ruby
HTTPI::Request.new(url: "http://example.org", query: { foo: "bar" })
=> #<HTTPI::Request:0x02b05598 @url=#<URI::HTTP:0x02b05188 URL:http://example.org>>
```

Expected behaviour would be
```ruby
HTTPI::Request.new(url: "http://example.org", query: { foo: "bar" })
=> #<HTTPI::Request:0x0579cbd8 @url=#<URI::HTTP:0x0579c890 URL:http://example.org?foo=bar>>
```

This PR adds `query` to ```Request::Attributes``` so that it is called in ```Request#mass_assign```.