doc: update correct variable of app ID (#688)

Author: luvsaxena1

docs/github-settings/6. deployment-environments.md

@@ -30,7 +30,7 @@ environments:
       protected_branches: true
       custom_branch_policies: false
     deployment_protection_rules:
-      - appId: 25112  
+      - app_id: 25112  
     variables:
       - name: MY_AWESOME_VAR
         value: '845705'