fix wrong option name in `dm.min_free_space` examples

Signed-off-by: Harald Albers <github@albersweb.de>
(cherry picked from commit 2623b3496ead7c275d2e54bdfcdab0eab528be51)

docs/reference/commandline/daemon.md

@@ -462,7 +462,7 @@ options for `zfs` start with `zfs`.
 
     Example use:
 
-        $ docker daemon --storage-opt dm.min_free_space_percent=10%
+        $ docker daemon --storage-opt dm.min_free_space=10%
 
 Currently supported options of `zfs`:
 

man/docker-daemon.8.md

@@ -487,7 +487,7 @@ pool and that should automatically resolve it. If loop devices are being
 used, then stop docker, grow the size of loop files and restart docker and
 that should resolve the issue.
 
-Example use: `docker daemon --storage-opt dm.min_free_space_percent=10%`
+Example use: `docker daemon --storage-opt dm.min_free_space=10%`
 
 ## ZFS options