Update codebox (#9430)

* updated the codeboxes in docs

* codebox change from json to http

docs/sources/reference/dashboard.md

@@ -24,7 +24,7 @@ When a user creates a new dashboard, a new dashboard JSON object is initialized
 
 > Note: In the following JSON, id is shown as null which is the default value assigned to it until a dashboard is saved. Once a dashboard is saved, an integer value is assigned to the `id` field.
 
-```
+```json
 {
   "id": null,
   "title": "New dashboard",

docs/sources/reference/sharing.md

@@ -43,7 +43,7 @@ You also get a link to service side rendered PNG of the panel. Useful if you wan
 
 Example of a link to a server-side rendered PNG:
 
-```
+```bash
 http://play.grafana.org/render/dashboard-solo/db/grafana-play-home?orgId=1&panelId=4&from=1499272191563&to=1499279391563&width=1000&height=500&tz=UTC%2B02%3A00&timeout=5000
 ```