Heya,
There hasn't been a whole lot of changes in the map format. So... just open up BrowEdit 3 > load the map > data\map.rsw > Edit ... > Change the rsw version from 0x206 to... 0x204 would be good enough. Or you could also just lower the build number from 214 to 185. You could lower it all the way down to 0x201 and it wouldn't change much at all (0x201 is the most common map format, practically any client can read this one).
Then just save the map.
(Edit: Updating your client is the proper way obviously, but if you're not ready to update yet, then the above will work just fine.)