Specs failure with libyaml 0.2.2

[bcardiff]

Extracted from https://circleci.com/gh/crystal-lang/crystal/20015

Failures:

  1) YAML serialization to_yaml does for bytes
     Failure/Error: "hello".to_slice.to_yaml.should eq("--- !!binary 'aGVsbG8=\n\n'\n")

       Expected: "--- !!binary 'aGVsbG8=\n\n'\n"
            got: "--- !!binary 'aGVsbG8=\n\n  '\n"

     # spec/std/yaml/serialization_spec.cr:335

Finished in 1:33 minutes
6890 examples, 1 failures, 0 errors, 4 pending

Failed examples:

crystal spec spec/std/yaml/serialization_spec.cr:334 # YAML serialization to_yaml does for bytes

Ref: In the past #6287 solved compatibility with 0.2.1

[straight-shoota]

For reference: this seems to be yaml/libyaml#119

Should be easy to fix using YAML.libyaml_version like in #6287