HTTP headers are not case-sensitive

[dbergami]

supertest.get('test').set('Cache-Control', 'xablau' ) comes as

headers: { 'cache-control: xablau' }

headers are always converted to lowercase

how can i keep it exactly as it was set

[JonoAugustine]

This seems to be an old issue, #350 #796, not sure why it's still happening (it's happening for me as well)