Updated to reflect API version 52

README.md

@@ -7,6 +7,5 @@ This is very much Work In Progress. Don't use this for production
 installations. Much of the filter API in OpenSMTPD is not yet stable,
 so this package is also subject to change.
 
-We have implemented Filter API version 51, because that's compatible with
-the most recent portable OpenSMTPD version available in Debian Jessie and
-Stretch (version 6.0.2p1).
+We have implemented Filter API version 52, because that's compatible with
+the most recent portable OpenSMTPD version (6.0.3p1).