Bump django from 2.1.2 to 2.1.15 (#3)

Bump django from 2.1.2 to 2.1.15

Author: p8ul

requirements.txt

@@ -2,7 +2,7 @@ certifi==2018.8.24
 chardet==3.0.4
 coverage==4.5.1
 coveralls==1.5.1
-Django==2.1.2
+Django==2.1.15
 django-cors-middleware==1.2.0
 django-extensions==1.7.1
 django-filter==2.0.0