yaml-0.8.21 test failures

[juhp]

from Stackage Nightly:

  test/Data/YamlSpec.hs:469: 
  1) Data.Yaml, empty input, parses as Null from file
       expected: Right Null
        but got: Left "YAML exception:\nYaml file not found: test/resources/empty.yaml"

  test/Data/YamlSpec.hs:477: 
  2) Data.Yaml, comment only input, parses as Null from file
       expected: Right Null
        but got: Left "YAML exception:\nYaml file not found: test/resources/empty2.yaml"

[snoyberg]

Should be fixed, sending a PR now. Thanks :)