Use buffer byte length at POST body

lib/client.js

@@ -80,7 +80,7 @@ client.prototype.request = function(method, path, params, callback){
     if(["POST", "PUT"].indexOf(http_options["method"]) >= 0){
         http_options["headers"] = {
             "Content-Type": params["contentType"] ? params["contentType"] : "application/json",
-            "Content-Length": body.length,
+            "Content-Length": Buffer.byteLength(body),
         };
     }