Bug in Validations.py under "validate_user" function

[k-naula97]

Issue is with the behavior of "validate_user" function in validations.py.
This script should validate usernames if they start with a letter only.

to fix this issue change:
if not re.match('^[a-z0-9._]*$', username) AND if username[0].isnumeric():

it should be:

if not re.match(r'^[A-Za-z0-9._]*$', username)
if not username[0].isalpha():