build: better naming for firebase token (#4742)

Changes the `MATERIAL2_FIREBASE_PRIVATE_KEY` to `MATERIAL2_DASHBOARD_FIREBASE_KEY` because it's confusing to just say that its for firebase.

Giving it a more explicit token as same as with the screenshots ensures that we have a structured & clean list of tokens in our CI settings.

Author: devversion

tools/gulp/util/firebase.ts

@@ -15,7 +15,7 @@ export function openFirebaseDashboardDatabase() {
       client_email: 'firebase-adminsdk-ch1ob@material2-dashboard.iam.gserviceaccount.com',
       // In Travis CI the private key will be incorrect because the line-breaks are escaped.
       // The line-breaks need to persist in the service account private key.
-      private_key: decode(process.env['MATERIAL2_FIREBASE_PRIVATE_KEY'])
+      private_key: decode(process.env['MATERIAL2_DASHBOARD_FIREBASE_KEY'])
     }),
     databaseURL: 'https://material2-dashboard.firebaseio.com'
   });