Spec: Added human flag to indices.get_upgrade

rest-api-spec/api/indices.get_upgrade.json

@@ -25,6 +25,11 @@
             "options" : ["open","closed"],
             "default" : "open",
             "description" : "Whether to expand wildcard expression to concrete indices that are open, closed or both."
+        },
+        "human": {
+            "type": "boolean",
+            "description": "Whether to return time and byte values in human-readable format.",
+            "default": false
         }
       }
     },