code: function(source, identifier, options) {
    const hash = crypto.createHash("md4");
  
    const contents = JSON.stringify({ source, options, identifier });
  
    hash.update(contents);
  
    return hash.digest("hex") + ".json";
  }
docs: Build the filename for the cached file
  
  @params {String} source  File source code
  @params {Object} options Options used
  
  @return {String}