Missing comma in index.json

Docker/hello-docker/index.json

@@ -11,7 +11,7 @@
       }
     ],
     "intro": {
-      "text": "intro.md"
+      "text": "intro.md",
       "courseData": "intro-course-data.sh",
       "credits": "This course was inpired by [Docker and Makefiles example from Ben Hall](https://github.com/BenHall/katacoda-scenarios/tree/master/1)"
     },