Bug fix: Install devtron & Ember Inspector in dev (#1698)

In the process of removing `electron-is-dev` the way that we determine
if we're in development environments changed, and as a result we need to
invert the conditional.

Fixes: #1697

forge/files/src/index.js

@@ -31,7 +31,7 @@ app.on('window-all-closed', () => {
 });
 
 app.on('ready', async () => {
-  if (app.isPackaged) {
+  if (!app.isPackaged) {
     try {
       require('devtron').install();
     } catch (err) {