`lmpt_port` corrected tio `lmtp_port`

This is such a bonkers error.  Would have actually just shown up if I
hadn't been in a try loop.

docs/courier-to-mailman3.md

@@ -34,3 +34,4 @@ This is our current version trying to communicate between courier and mailman3.
   * Catch exception, log based on that?
   * Hm, go with bare "Exception"...  The catch wasn't what was failing.
   * Let's try that instead?
+* Oh man...  Variable not properly defined (or more derferenced.)

source/courier-to-mailman3.py

@@ -36,7 +36,7 @@ try:
     # class smtplib.LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None)
     logger.info('lmtp_port: %s', lmtp_port)
     lmtp = smtplib.LMTP(lmtp_host, int(lmtp_port))
-    logger.info('lmtp_port (lmtp setup): %s', lmpt_port)
+    logger.info('lmtp_port (lmtp setup): %s', lmtp_port)
 
     try:
         # Unfortunately qmail sends to local bare LF for end line, while