Multi byte upcase_first polyfill

mutlibyte_upcase_first.rb

class String
  # polyfill until Rails 5, with support for multi-byte chars
  # https://glaucocustodio.github.io/2016/05/19/rails-5-new-upcase-first-method/
  # https://coderwall.com/p/b74yda/rails-upcase-downcase-for-non-ascii-strings
  unless method_defined? :upcase_first
    def upcase_first
      return self if length == 0
      self.mb_chars[0].upcase.mb_chars.concat(self[1..-1]).to_s
    end
  end
end