Support for the Ruby 2.4 series has ended. See here for reference.
# File psych/lib/psych/core_ext.rb, line 22 def psych_yaml_as url return if caller[0].end_with?('rubytypes.rb') if $VERBOSE warn "#{caller[0]}: yaml_as is deprecated, please use yaml_tag" end Psych.add_tag(url, self) end