Incorrect kafka example event and marshaling

[LegNeato]

Incorrect kafka example event and marshaling.

#385 changed the logic and example data. In that PR, there was a comment "Array and slice values encode as JSON arrays, except that []byte encodes as a base64-encoded string, and a nil slice encodes as the null JSON value."

So while the Go code was changed to []byte, the example event checked in doesn't have the value as a base64-encoded string and instead includes a json array.

Either the Go code should change to an Array or slice or the example event should be changed to include a base64 string. I am not sure which is correct (I haven't used this event type so I don't know what AWS sends), but they currently do not match--which is why the assertion had to be incorrectly deleted.

This is breaking code generation in calavera/aws-lambda-events#39 as we actually assert the event can be round-tripped and use the aforementioned byte[] encoding.

[LegNeato]

@ianpyw

[LegNeato]

Adding @keshayad so he is aware as he merged the PR.

[LegNeato]

This was fixed by #392, thank you!