Update and rename apps/meteor/app.json to app.json

Heroku app.json file needs to be in root folder

app.json

@@ -2,11 +2,12 @@
   "name": "Rocket.Chat",
   "description": "Have your own open-source Slack-like online chat platform.",
   "repository": "https://github.com/RocketChat/Rocket.Chat",
-  "logo": "https://raw.githubusercontent.com/RocketChat/Rocket.Chat/master/public/images/logo/1024x1024.png",
+  "logo": "https://raw.githubusercontent.com/RocketChat/Rocket.Chat.Artwork/master/Logos/2020/png/logo-horizontal-red.png",
   "keywords": ["meteor", "social", "community", "chat"],
   "website": "https://rocket.chat",
   "env": {
     "BUILDPACK_URL": "https://github.com/RocketChat/meteor-buildpack-horse.git",
+    "METEOR_APP_DIR": "apps/meteor/",
     "HEROKU_APP_NAME": {
       "description": "Please re-enter your App Name from the top.",
       "required": true