uidMappings: change order of fields for clarity

"man 7 user_namespaces" explains the format of uid_map and gid_map:
    <containerID> <hostID> <mapSize>

The order of map entries in JSON does not matter. But for the clarity of
the spec, I find it easier to understand if the order of the JSON fields is
the same as the order of the fields in the underlying uid_map/gid_map
files.

I am about to file a PR in runtime-tools because the fields in
uid_map/gid_map were parsed in the wrong order.

Signed-off-by: Alban Crequy <alban@kinvolk.io>

config-linux.md

@@ -82,8 +82,8 @@ If a `namespaces` field contains duplicated namespaces with same `type`, the run
 
 Each entry has the following structure:
 
-* **`hostID`** *(uint32, REQUIRED)* - is the starting uid/gid on the host to be mapped to *containerID*.
 * **`containerID`** *(uint32, REQUIRED)* - is the starting uid/gid in the container.
+* **`hostID`** *(uint32, REQUIRED)* - is the starting uid/gid on the host to be mapped to *containerID*.
 * **`size`** *(uint32, REQUIRED)* - is the number of ids to be mapped.
 
 The runtime SHOULD NOT modify the ownership of referenced filesystems to realize the mapping.
@@ -94,15 +94,15 @@ Note that the number of mapping entries MAY be limited by the [kernel][user-name
 ```json
     "uidMappings": [
         {
-            "hostID": 1000,
             "containerID": 0,
+            "hostID": 1000,
             "size": 32000
         }
     ],
     "gidMappings": [
         {
-            "hostID": 1000,
             "containerID": 0,
+            "hostID": 1000,
             "size": 32000
         }
     ]