fix username generator

[avil13]

Closes #34

[avil13]

fix

[sdushantha]

I really like your take on this problem, but I think it would be better to use this instead:

84c84
<     USERNAME=$(head /dev/urandom | tr -dc "[:alnum:]" | cut -c1-11 | tr "[:upper:]" "[:lower:]")
---
>     USERNAME=$(head /dev/urandom | LC_ALL=C tr -dc "[:alnum:]" | cut -c1-11 | tr "[:upper:]" "[:lower:]")

By using LC_ALL=C, it fixes the issue with tr on macOS.
It also allows us to keep the randomness of the username, whereas in your fix it's not random because you are using date +%s