Remove Django 3.0 DeprecationWarning

[rhenter]

Change ugettext_lazy by gettext_lazy to remove Django 3.0 DeprecationWarning

• Log Sample:

.../lib/python3.7/site-packages/oauth2_provider/models.py:41: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (CLIENT_CONFIDENTIAL, _("Confidential")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:42: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (CLIENT_PUBLIC, _("Public")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:50: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (GRANT_AUTHORIZATION_CODE, _("Authorization code")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:51: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (GRANT_IMPLICIT, _("Implicit")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:52: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (GRANT_PASSWORD, _("Resource owner password-based")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:53: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  (GRANT_CLIENT_CREDENTIALS, _("Client credentials")),
.../lib/python3.7/site-packages/oauth2_provider/models.py:67: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().
  blank=True, help_text=_("Allowed URIs list, space separated"),

[coveralls]

Pull Request Test Coverage Report for Build 1234

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.725%

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Totals
Change from base Build 1227:	0.0%
Covered Lines:	1257
Relevant Lines:	1327

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💛 - Coveralls