Dechunk HTTP requests by default (#11)

ProxyManager already has all the Request body's data. There is no never
a need to use chunked transfer encoding to the upstream process.

proxy/process.go

@@ -178,7 +178,7 @@ func (p *Process) ProxyRequest(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
-	req.Header = r.Header
+	req.Header = r.Header.Clone()
 	resp, err := client.Do(req)
 	if err != nil {
 		http.Error(w, err.Error(), http.StatusBadGateway)