fix install param null bug & build

Author: icebob

dist/vue-websocket.js

@@ -1,6 +1,6 @@
 {
   "name": "vue-websocket",
-  "version": "0.2.1",
+  "version": "0.2.2",
   "description": "Websocket handler for Vue.js",
   "homepage": "https://github.com/icebob/vue-websocket",
   "main": "dist/vue-websocket.js",

dist/vue-websocket.js.map

@@ -6,7 +6,7 @@ export default {
 
 		let socket;
 
-		if (typeof connection === "object")
+		if (connection != null && typeof connection === "object")
 			socket = connection;
 		else
 			socket = IO(connection || "", opts);