Added "improvedOnboarding" labs flag

refs https://github.com/TryGhost/Team/issues/1294

- used for working on changes to the setup flow and launch wizard

core/shared/labs.js

@@ -31,7 +31,8 @@ const ALPHA_FEATURES = [
     'urlCache',
     'beforeAfterCard',
     'tweetGridCard',
-    'membersActivityFeed'
+    'membersActivityFeed',
+    'improvedOnboarding'
 ];
 
 module.exports.GA_KEYS = [...GA_FEATURES];