Update README.md

[alok8bb]

• [x] I carefully read the contribution guidelines and agree to them.
• [ ] I have tested the API against NewPipe.

Why? I was adding NewPipeExtractor to my project and after adding maven repository I got Failed to resolve: com.github.TeamNewPipe.NewPipeExtractor:0.22.1 error. After searching for some time I found out that the tag part of maven repository is changed and I updated the implementation URL according to jitpack website, this fixed the problem.

Changes Most people copy and paste the implementation block from README, therefore updated it with Gradle 6.8's dependency management improvements. and update implementation string.

Feel free to edit as you wish. Thanks