Update pillow from 5.0.0 to 6.0.0

Author: pyup-bot

requirements.txt

@@ -12,7 +12,7 @@ django-rest-auth==0.9.5
 furl==2.0.0
 future==0.17.1
 jsmin==2.2.2
-Pillow==5.0.0
+Pillow==6.0.0
 psycopg2==2.7.3.1
 Pygments==2.2.0
 python-decouple==3.1