chore(deps): introduce open and remove opn (#1865)

Because opn was renamed to open.

Author: hiroppy

lib/utils/runOpen.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const open = require('opn');
+const open = require('open');
 
 function runOpen(uri, options, log) {
   // https://github.com/webpack/webpack-dev-server/issues/1990

package-lock.json

@@ -50,7 +50,7 @@
     "ip": "^1.1.5",
     "killable": "^1.0.1",
     "loglevel": "^1.6.2",
-    "opn": "^5.5.0",
+    "open": "^6.2.0",
     "p-retry": "^3.0.1",
     "portfinder": "^1.0.20",
     "schema-utils": "^1.0.0",