Specify maxResponseHeadersSize when initializing HTTP client (#126)

* Specify `maxResponseHeadersSize` when initializing HTTP client

Update to be compatible with newer Chronos versions that have an
additional argument when instantiating `HttpClientRequestRef`.

* Specify max header size implicitly to remain compatible with old Chronos

graphql/httpclient.nim

@@ -274,7 +274,7 @@ proc sendRequest*(ctx: GraphqlHttpClientRef, query: string,
       HttpClientRequestRef.new(
         ctx.session, ctx.address,
         ctx.meth, ctx.version, {},
-        newHeaders, body
+        headers = newHeaders, body = body
       )
 
     let resp = await request.send()