Fix note alert box in convdev doc

The `note` alert box within the convdev doc was improperly formatted. 

doc/user/instance_statistics/convdev.md

@@ -2,7 +2,7 @@
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/30469) in GitLab 9.3.
 
-NOTE: **NOTE**
+NOTE: **Note:**
 Your GitLab instance's [usage ping](../admin_area/settings/usage_statistics.md#usage-ping-core-only) must be activated in order to use this feature.
 
 The Conversational Development Index (ConvDev Index) gives you an overview of your entire