Handle OSX encoding a bit better

[bil-bas]

A better solution is provided in this workaround for Shoes:

shoes/shoes-deprecated#163 (comment)

class Encoding
  %w[ASCII_8BIT US_ASCII UTF_16BE UTF_16LE UTF_32BE UTF_32LE].each do |ec|
    eval "#{ec} = '#{ec.sub '_', '-'}'"
  end unless RUBY_PLATFORM =~ /linux/
end 

Though might as well use #const_set rather than #eval