Check minimum suported Grafana version

[jonyrock]

Now we declare in plugin.json that we support 3.x.x:
https://github.com/grafana/kentik-app/blob/master/src/plugin.json#L113

Is it true?

[sankerust]

There is no specific error for unsupported grafana version.
I tried to use the app on grafana 5.2.4. and it didn't work properly, giving different errors.

[jonyrock]

@sankerust so this plugin doesn't work on 5.2.4 ?