fix bug in dashboard validation

lib/api/dash.js

@@ -19,10 +19,10 @@ var validate_dashboard = function(dashboard){
     }
 
     for(var i in dashboard['graphs']){
-	if(!dashboard['graphs']['title']){
+	if(!dashboard['graphs'][i]['title']){
 	    throw new Error(util.format('`dashboard["graphs"][%s]["title"]` is missing', i));
 	}
-	if(!dashboard['graphs']['definition']){
+	if(!dashboard['graphs'][i]['definition']){
 	    throw new Error(util.format('`dashboard["graphs"][%s]["definition"]` is missing', i));
 	}
     }