change `username` requests to just `user`

story time

i was attempting to get a api key, and like the somewhat-smart person i am, i decided to check the docs!

turns out these are really deprecated lol.

considering making a issue in the main elixi.re repository to standardize use of user vs username throughout the codebase. pretty conflicting imo.

gonna try and update these docs more personally but it's almost midnight so not gonna go it right now :) here's just a small fix.