Fix parsing error when self describing data is not a map

[adatzer]

Currently, the type assumed for Data in SelfDescribingData struct is a map.
This results in error (Error unmarshaling context JSON) when trying to parse unstruct events or contexts having a different type (e.g. json array) for their data.
Error can be reproduced in tests when replacing the contextString with something like:

var contextsString = `{"schema":"iglu:com.snowplowanalytics.snowplow/contexts/jsonschema/1-0-0","data":[{"schema":"iglu:com.acme.test/testing/jsonschema/1-0-0","data":["aa","bb"]}]}`

[colmsnowplow]

Thanks for raising - according to our documentation, arrays at the top level aren't valid. The do pass validation, but I consider that to be the problem underlying this issue. I've created a ticket against the enrich repo: snowplow/enrich#749

Closing this one