fix image spec JSON example

Signed-off-by: haining.cao <haining.cao@daocloud.io>

image/spec/v1.1.md

@@ -144,7 +144,7 @@ Here is an example image JSON file:
             "/var/job-result-data": {},
             "/var/log/my-app-logs": {},
         },
-        "WorkingDir": "/home/alice",
+        "WorkingDir": "/home/alice"
     },
     "rootfs": {
       "diff_ids": [

image/spec/v1.2.md

@@ -144,7 +144,7 @@ Here is an example image JSON file:
             "/var/job-result-data": {},
             "/var/log/my-app-logs": {},
         },
-        "WorkingDir": "/home/alice",
+        "WorkingDir": "/home/alice"
     },
     "rootfs": {
       "diff_ids": [

image/spec/v1.md

@@ -151,7 +151,7 @@ Here is an example image JSON file:
             "/var/job-result-data": {},
             "/var/log/my-app-logs": {},
         },
-        "WorkingDir": "/home/alice",
+        "WorkingDir": "/home/alice"
     }
 }
 ```