Add toUpperCase/toLowerCase sanitizers to validation chain

[dxmaxwell]

I am attempting to simplify my existing validation logic by using this library. However, I soon realized that my code uses trim() and toUpperCase() in many places, but express-validator does not have a sanitizer that corresponds to toUpperCase().

For now I have used a custom sanitizer, but this seems like something that would be generally useful.

[liqiang372]

What's the status of this issue? It's been open for over 2 years. I can help if it's not been taken care of yet, @gustavohenke.

[chinesedfan]

Closed by #899.

[gustavohenke]

Out in v6.7.0!