utils: hash: Use hashlib for pbkdf2

!!!

This is a backport of a commit from the master branch to fix
compatibility with werkzeug 2.1+

!!!

werkzeug 2.1 will deprecate `pbkdf2_bin` and recommends
pbkdf2_hmac as an alternative.

Adjust function invocation and use named args to avoid
confusion.

Compare:
https://werkzeug.palletsprojects.com/en/2.0.x/utils/#werkzeug.security.pbkdf2_bin
-> Will be gone in werkzeug 2.1
https://docs.python.org/3/library/hashlib.html#hashlib.pbkdf2_hmac
-> Available since Python 3.4

isso/utils/hash.py

@@ -3,7 +3,7 @@
 import codecs
 import hashlib
 
-from werkzeug.security import pbkdf2_bin as pbkdf2
+from hashlib import pbkdf2_hmac as pbkdf2
 
 
 def _TypeError(name, expected, val):
@@ -68,7 +68,8 @@ def __init__(self, salt=None, iterations=1000, dklen=6, func="sha1"):
         self.func = func
 
     def compute(self, val):
-        return pbkdf2(val, self.salt, self.iterations, self.dklen, self.func)
+        return pbkdf2(hash_name=self.func, password=val, salt=self.salt,
+                      iterations=self.iterations, dklen=self.dklen)
 
 
 def new(conf):