fix(WebRTCService): each peer can open a door to the webChannel instead to have only one door availa

The join key equals to webChannel.id plus peerId.

Author: kalitine

dist/netflux.es2015.js

@@ -349,7 +349,7 @@
     }
 
     open (webChannel, onChannel, options = {}) {
-      let key = webChannel.id
+      let key = webChannel.id + webChannel.myId
       let settings = Object.assign({}, this.settings, options)
       // Connection array, because several connections may be establishing
       // at the same time

dist/netflux.js

@@ -587,7 +587,7 @@ return /******/ (function(modules) { // webpackBootstrap
 
 	      var options = arguments.length <= 2 || arguments[2] === undefined ? {} : arguments[2];
 
-	      var key = webChannel.id;
+	      var key = webChannel.id + webChannel.myId;
 	      var settings = Object.assign({}, this.settings, options);
 	      // Connection array, because several connections may be establishing
 	      // at the same time