Normalize the encoding names for Latin-1 and UTF-8 to
'latin-1' and 'utf-8'.

These are optimized in the Python Unicode implementation
to result in more direct processing, bypassing the codec
registry.

Also see issue11303.
diff --git a/Lib/asynchat.py b/Lib/asynchat.py
index 6558512..2199d1b 100644
--- a/Lib/asynchat.py
+++ b/Lib/asynchat.py
@@ -75,7 +75,7 @@
     # sign of an application bug that we don't want to pass silently
 
     use_encoding            = 0
-    encoding                = 'latin1'
+    encoding                = 'latin-1'
 
     def __init__ (self, sock=None, map=None):
         # for string terminator matching