Crashes on improperly formatted YAML

[edahlseng]

When attempting to parse improperly formatted YAML, pretty-swag crashes instead of returning an error in the callback. This can be tested by attempting to generate output for this example:

paths:
  "/{test}/":
      parameters:
        - $ref: "#/parameters/test"
    post:
      summary: This is a test file

(Side note: I know I've created several issues already today... let me know if you'd like a hand with any of them!)

[twskj]

This one should be an easy fix. I'll work on it today. Also thanks for offering help, any PR is welcome :-)

[twskj]

rolled-out