pbrd: fix show pbr map detail json

'detail' and 'josn' keyword is given as an optional parameter
for cli arguments. Hence 'detail' keyword was consider as a
pbr 'name' for "show pbr map detail json" command.

Before Fix:

```
cumulus#
cumulus# show pbr map detail json
[
]
cumulus#
```

After Fix:
```
cumulus# show pbr map detail json
[
  {
    "name":"MAP1",
    "valid":false,
    "policies":[
      {
        "id":1,
        "sequenceNumber":10,
        "ruleNumber":309,
        "vrfUnchanged":false,
        "installed":false,
        "installedReason":"Invalid Src or Dst",
        "vrfName":"default"
      }
    ]
  }
]
cumulus#
```

Ticket:#3638600

Issue:3638600

Testing: UT done

Signed-off-by: Sindhu Parvathi Gopinathan's <sgopinathan@nvidia.com>
(cherry picked from commit d621c36)

pbrd/pbr_vty.c

@@ -1062,7 +1062,7 @@ static void vty_json_pbr_map(json_object *j, struct vty *vty,
 
 DEFPY (show_pbr_map,
 	show_pbr_map_cmd,
-	"show pbr map [NAME$name] [detail$detail|json$json]",
+	"show pbr map [NAME$name] [detail$detail] [json$json]",
 	SHOW_STR
 	PBR_STR
 	"PBR Map\n"