Support non-printable/emoji characters in comments

[brianmhunt]

Following the merging of #368, non-printable characters encountered by js-yaml seem to throw an error.

I suspect that this is a breaking change that will affect a number of people who happen to have e.g. emoji in comments when they upgrade to 3.10.

Though ignoring non-printables in comments would appears to be a breach of spec, I feel that they should be acceptable (i.e. ignored), as this fix would not substantively affect the parsing or output. I noted that e.g. the Python yaml parser ignores emoji in comments.

[brianmhunt]

I'm closing this because it's only reproducible on circle-ci, so I suspect it may be a package management issue. Will re-open if reproducible otherwise.