fix: replaced md4 with blake2b

(cherry picked from commit 167247de134ab2b03e03bfd6c579c86d7ce59e4a)

common/djangoapps/util/memcache.py

@@ -14,9 +14,9 @@ def fasthash(string):
     """
     Hashes `string` into a string representation of a 128-bit digest.
     """
-    md4 = hashlib.new("md4")
-    md4.update(string.encode('utf-8'))
-    return md4.hexdigest()
+    blake2b = hashlib.new("blake2b", digest_size=16)
+    blake2b.update(string.encode('utf-8'))
+    return blake2b.hexdigest()
 
 
 def cleaned_string(val):