Update work-with-networks.md

The value of the Subnet and Gateway properties didn't match the command-line argument.

Signed-off-by: David M. Karr <davidmichaelkarr@gmail.com>
(cherry picked from commit a54c3fbb8aa024c477864a0614506da3ea185839)

docs/userguide/networking/work-with-networks.md

@@ -208,8 +208,8 @@ $ docker network inspect isolated_nw
             "Driver": "default",
             "Config": [
                 {
-                    "Subnet": "172.21.0.0/16",
-                    "Gateway": "172.21.0.1/16"
+                    "Subnet": "172.25.0.0/16",
+                    "Gateway": "172.25.0.1/16"
                 }
             ]
         },