rpc.js: removed Buffer.from

There hasn't Buffer Object in react native environment.

lib/browser/rpc.js

@@ -180,7 +180,7 @@ function makeRequest(url, data) {
     if (global.__debug__) {
         let request = global.__debug__.require('sync-request');
         let response = request('POST', url, {
-          body: Buffer.from(JSON.stringify(data)),
+          body: JSON.stringify(data),
           headers: {
             "Content-Type": "text/plain;charset=UTF-8"
           }