Some emojis are incorrectly not considered printable

[taliastocks]

Some emojis are incorrectly not considered printable, e.g. "😂" will always be quoted as "\U0001F602" even if encoder.unicode is enabled.

[hschne]

FYI, there is a PR against Psych (a Ruby wrapper for Libyaml) that contains some code that may be useful for the eventual fix.

ruby/psych#508