Fix samples

docs/samples/payment.js

@@ -24,18 +24,22 @@ const payment = {
   }
 };
 
+function quit(message) {
+  console.log(message);
+  process.exit(0);
+}
+
+function fail(message) {
+  console.error(message);
+  process.exit(1);
+}
+
 api.connect().then(() => {
   console.log('Connected...');
-  api.preparePayment(address, payment, instructions).then(txJSON => {
+  return api.preparePayment(address, payment, instructions).then(prepared => {
     console.log('Payment transaction prepared...');
-    const signedTransaction = api.sign(txJSON, secret).signedTransaction;
+    const {signedTransaction} = api.sign(prepared.txJSON, secret);
     console.log('Payment transaction signed...');
-    api.submit(signedTransaction).then(response => {
-      console.log(response);
-      process.exit(0);
-    }).catch(error => {
-      console.log(error);
-      process.exit(1);
+    api.submit(signedTransaction).then(quit, fail);
   });
-  });
-});
+}).catch(fail);

src/index.js

@@ -5,7 +5,12 @@
 // Enable core-js polyfills. This allows use of ES6/7 extensions listed here:
 // https://github.com/zloirock/core-js/blob/fb0890f32dabe8d4d88a4350d1b268446127132e/shim.js#L1-L103
 /* eslint-enable max-len */
-require('babel-core/polyfill');
+
+// In node.js env, polyfill might be already loaded (from any npm package),
+// that's why we do this check.
+if (!global._babelPolyfill) {
+  require('babel-core/polyfill');
+}
 
 const _ = require('lodash');
 const EventEmitter = require('events').EventEmitter;