Bumped version of python-slugify to 4 to avoid versioning issues.

Author: BethanyG

cbv3_django_prototype/requirements/base.txt

@@ -1,7 +1,7 @@
 
 argon2-cffi==19.1.0            # https://github.com/hynek/argon2_cffi
 Pillow==6.1.0                  # https://github.com/python-pillow/Pillow
-python-slugify==3.0.3          # https://github.com/un33k/python-slugify
+python-slugify==4.0.0          # https://github.com/un33k/python-slugify
 pytz==2019.2                   # https://github.com/stub42/pytz
 redis==3.3.8                   # https://github.com/antirez/redis