chore(deps): update dependency djangorestframework to v3.15.2 [security]

Author: renovate[bot]

requirements.txt

@@ -14,7 +14,7 @@ django-environ==0.11.2
 # django-rest-auth==0.9.3
 # django-slack-oauth==1.4.3
 django-webpack-loader==0.7.0
-djangorestframework==3.14.0
+djangorestframework==3.15.2
 enum34==1.1.10
 facepy==1.0.12
 gunicorn==19.10.0