requirements: Update bencode.py to latest version

Update to the latest version for Python 3 compatibiity.

requirements.txt

@@ -3,7 +3,7 @@ Django==1.11.18
 IPy==0.83
 Markdown==2.6.10
 MarkupSafe==0.23
-bencode.py==1.2.0
+bencode.py==2.0.0
 django-countries==5.0
 jsmin==2.2.2
 pgpdump==1.5