fix #162 - Changing Username doesn't update the User model username

[Kaushal-Dhungel]

Describe your changes :

I worked on the issue #162 because changing UserProfile's username was not updating the User model username.

Type of change :

• [x] Bug fix

Preview (Screenshots) :

If it is possible, please link screenshots of your changes preview !

Checklist:

• [x] I have read the Code Of Conduct document.
• [x] I have read the CONTRIBUTING document.
• [x] I have performed a self-review of my own.
• [x] I have tagged my reviewers below.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] My changes generate no new warnings.
• [x] I have added tests that prove my fix is effective or that my feature works.
• [x] All new and existing tests passed.

Reviewers

@PraveenMalethia @codyseibert

[Kaushal-Dhungel]

The commit message should have been "fix #162 ... " but I wrote, "fix #142 ...". Is this a problem??