Correct bug when passing non-string query params.

When passing anything other than a String, will stacktrace. For
instance:

new RequestBuilder().build {
    uri = "127.0.0.1:8080/sample.com"
    query = [
        myQuery: true
    ]
}

Will break because true is not a String.
Merge pull request #4 from aaron-brown/query_parameter_bug

Correct bug when passing non-string query params.