addTransaction() docstring typo fix -> request

Author: altendky

pymodbus/transaction.py

@@ -324,7 +324,7 @@ def _recv(self, expected_response_length, full):
     def addTransaction(self, request, tid=None):
         """ Adds a transaction to the handler
 
-        This holds the requets in case it needs to be resent.
+        This holds the request in case it needs to be resent.
         After being sent, the request is removed.
 
         :param request: The request to hold on to