Add black to dev dependencies

Author: char

Pipfile

@@ -4,6 +4,7 @@ url = "https://pypi.org/simple"
 verify_ssl = true
 
 [dev-packages]
+black = "*"
 
 [packages]
 httpx = "*"
@@ -20,3 +21,6 @@ bcrypt = "*"
 
 [requires]
 python_version = "3.8"
+
+[pipenv]
+allow_prereleases = true