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/http/client.py b/Lib/http/client.py
index 36b7349..8ad7cb6 100644
--- a/Lib/http/client.py
+++ b/Lib/http/client.py
@@ -697,7 +697,7 @@
         self.send(connect_bytes)
         for header, value in self._tunnel_headers.items():
             header_str = "%s: %s\r\n" % (header, value)
-            header_bytes = header_str.encode("latin1")
+            header_bytes = header_str.encode("latin-1")
             self.send(header_bytes)
         self.send(b'\r\n')
 
@@ -937,7 +937,7 @@
         values = list(values)
         for i, one_value in enumerate(values):
             if hasattr(one_value, 'encode'):
-                values[i] = one_value.encode('latin1')
+                values[i] = one_value.encode('latin-1')
             elif isinstance(one_value, int):
                 values[i] = str(one_value).encode('ascii')
         value = b'\r\n\t'.join(values)