Fixed setting providers to the right object

qt.js

@@ -3,6 +3,7 @@
     QtProvider.prototype.send = function(payload) {
         navigator.qt.postData(JSON.stringify(payload));
     };
+
     Object.defineProperty(QtProvider.prototype, "onmessage", {
         set: function(handler) {
             navigator.qt.onmessage = handler;
@@ -10,6 +11,7 @@
     }); 
 
     if(typeof(web3) !== "undefined" && web3.providers !== undefined) {
-        web3.QtProvider = QtProvider;
+        web3.providers.QtProvider = QtProvider;
     }
 })();
+