yaml bumper does not handle multi-document yamls

[Nick Mitchell]

Hello there. It looks like the bumper logic here assumes that the parsed documents are objects, not arrays of objects. However, for multi-document yaml files, this is not the case.

For example:

version: 1.0.0
---
version: 1.0.0

results this error

ERROR expected a single document in the stream, but found more

[Lars Kappert]

Closing this since #25 is closed as well.