Get 'SocialLoginSerializer' in app_settings.py if it's customized

[cafitac]

I need to customizing 'SocialLoginSerializer', but i can't.
So I want to would be possible through add this feature what get custom 'SocialLoginSerializer' :>

[coveralls]

Coverage increased (+0.004%) to 96.048% when pulling 7f75752 on leensungzero:custom-registration-serializers into 624ad01 on Tivix:master.

[BarnabasSzabolcs]

Hi,
as a user of rest-auth, thanks for the contribution!
This repo is not maintained anymore, so the development moved to dj-rest-auth. (reference: #568)
It may be best, if you move this PR there. (and upgrade to using dj_rest_auth)

new repo link: https://github.com/jazzband/dj-rest-auth (I'm not the upkeeper of that repo, it just makes sense for me to help you merge your PR)

Many Thanks,
Barney