Previously doing `pipenv install "django-rest-auth[with_social]==0.8.2` would
lose the extra information and if you edited the Pipfile by hand to
```
[[source]]
url = "https://pypi.python.org/simple"
verify_ssl = true
[packages.django-rest-auth]
version = "==0.8.2"
extras = [ "with_social",]
```
`pipenv update` would break with a malformed pip command.