Make transformers install check positive
# What does this PR do?

When transformers is correctly installed, I feel you should get a positive message. It's called huggingface not angryface, after all ;-) 

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dimiss the other checks if that's the case).

## Who can review?

Anyone in the community is free to review the PR once the tests have passed. 
Given this concerns the documentation, mentioning @sgugger