Switch to opn package for opening url

fixes #593

Author: SpaceK33z

bin/webpack-dev-server.js

@@ -1,7 +1,7 @@
 #!/usr/bin/env node
 
 var path = require("path");
-var open = require("open");
+var open = require("opn");
 var fs = require("fs");
 
 // Local version replaces global one

package.json

@@ -11,7 +11,7 @@
     "connect-history-api-fallback": "^1.2.0",
     "express": "^4.13.3",
     "http-proxy-middleware": "~0.17.1",
-    "open": "0.0.5",
+    "opn": "4.0.2",
     "serve-index": "^1.7.2",
     "sockjs": "^0.3.15",
     "sockjs-client": "^1.0.3",