Variable version added in gradle(app) file

[geekanamika]

Description

As a developer, I need to update dependency version many times. Hence, keeping all variables at one place is very easy to maintain.

Fixes #1310

Type of Change:

• Quality Assurance

How Has This Been Tested?

Successful run of ./gradlew assembleDebug

Checklist:

Delete irrelevant options.

• [ ] I have performed a self-review of my own code or materials
• [ ] I have commented my code or provided relevant documentation, particularly in hard-to-understand areas

Code/Quality Assurance Only

• [ ] My changes generate no new warnings

[geekanamika]

@mayburgos @m-murad @Rimjhim28 Can you please merge it? It already has 2 approving reviews & considerably small change.