Fix collection selection in Grafana 4.
In Grafana 4, the lodash library was updated from 2.4.2 to 4.15.0, in which the
_.findWhere alias no longer exists, causing errors when trying to select an collection in Grafana 4, see issue #19 (closed).
This simply changes the call to use
_.find, which yields identical behaviour. Also, since
_.find already existed in previous lodash versions, the plugin still works as before on older Grafana versions.