The ObjectMapper used by GrafanaClient should enable ACCEPT_SINGLE_VALUE_AS_ARRAY

[bascarsija]

Otherwise deserialization will fail (against Grafana 4.6.2, at least) due to an apparently flexible representation of certain fields as either a string or an array of strings (e.g. "tags").

Please note that I have created a fork that already implements this, and can produce a PR if this functionality is desired in the main code base.