btrfs-progs: docs: fix typo in mkfs.btrfs manual page

"it's up to the user to changed" -> "it's up to the user to change".

Pull-request: #1066
Signed-off-by: David Sterba <[email protected]>

Author: gpenz

Documentation/mkfs.btrfs.rst

@@ -58,7 +58,7 @@ OPTIONS
 
         Default on a single device filesystem is *DUP* and is recommended for metadata
         in general. The duplication might not be necessary in some use cases and it's
-        up to the user to changed that at mkfs time or later. This depends on hardware
+        up to the user to change that at mkfs time or later. This depends on hardware
         that could potentially deduplicate the blocks again but this cannot be detected
         at mkfs time.