docs: declarative test demo is only for LB 3.x (#848)

Specify that the declarative test demo is only for LoopBack 3.x

pages/en/community/Declarative-test-demo.md

@@ -4,7 +4,7 @@ keywords: automation, e2e, example, loopback, mocha, test
 tags: [community_project]
 sidebar: community_sidebar
 permalink: /doc/en/community/Declarative-test-demo.html
-summary: Example application that demonstrates using lb-declarative-e2e-test to write tests in an object definition style.
+summary: Example LoopBack 3.x application that demonstrates using lb-declarative-e2e-test to write tests in an object definition style.
 ---
 
 ## Links
@@ -17,6 +17,8 @@ Library used:
 
 ## Overview
 
+This community-contributed component/example is for LoopBack 3.x
+
 This project showcase the different features of [`lb-declarative-e2e-test`](https://www.npmjs.com/package/lb-declarative-e2e-test):
 - Test hooks: `before`, `beforeEach`, `after`, `afterEach`
 - Test `only` / `skip`
@@ -75,3 +77,4 @@ npm run test-watch
 ## Requirements
 
 - Node >= 8
+- LoopBack 3.x