def to_file(file, key = nil, jwe = nil)
      return File.binwrite(file, to_binary(key, jwe))
    end
def to_file(file, key = nil, jwe = nil)
      return File.binwrite(file, to_binary(key, jwe))
    end
Calls {JOSE::JWK.to_binary JOSE::JWK.to_binary} on a {JOSE::JWK JOSE::JWK} and then writes the binary to `file`.

 @param [String] file
 @param [String] key
 @param [JOSE::JWE] jwe
 @return [Fixnum] bytes written