setup: make chardet a mandatory dependency

It was made mandatory in 9685f50a69d0. At that time it seemed like it always
were present due to indirect dependencies, but apparently that is no longer the
case.

setup.py

@@ -73,6 +73,7 b' requirements = ['
     "paginate_sqlalchemy >= 0.3.0, < 0.4",
     "bcrypt >= 3.1.0, < 3.2",
     "pip >= 20.0, < 999",
+    "chardet >= 3",
 ]
 
 dependency_links = [