Remove trailing comma in config_schema.json (#279)

Author: estan

config_schema.json

@@ -107,7 +107,7 @@
           "cssclass": "highlight jumbotron"
         },
         "tables": null,
-        "break-on-newline": true,
+        "break-on-newline": true
       },
       "description": "[Markdown 2 options](https://github.com/trentm/python-markdown2/wiki/Extras) for the descriptions. `description_is_markdown` must be true for this to have any effect.\n\n**WARNING**\nAdding an extra, even if the value is false, will activate it. For example `{\"break-on-newline\": false}` will activate the `break-on-newline` extra.",
       "examples": [