#19485: clarify get_param example.

Patch by Vajrasky Kok.
diff --git a/Lib/email/message.py b/Lib/email/message.py
index 5020a03..f43a380 100644
--- a/Lib/email/message.py
+++ b/Lib/email/message.py
@@ -636,7 +636,7 @@
         If your application doesn't care whether the parameter was RFC 2231
         encoded, it can turn the return value into a string as follows:
 
-            param = msg.get_param('foo')
+            rawparam = msg.get_param('foo')
             param = email.utils.collapse_rfc2231_value(rawparam)
 
         """