message: Compile to es5 when options.js.compile.target equals es5
diff: @@ -55,7 +55,8 @@ export async function build(
  const compiledToES5 = (options.js === undefined) ?
  false :
  - options.js.compile === true || options.js.compile === 'es5';
  + options.js.compile === true || options.js.compile === 'es5' ||
  + (options.js.compile && options.js.compile.target === 'es5');
  if (compiledToES5) {
  buildStream =
  buildStream.pipe(polymerProject.addCustomElementsEs5Adapter());
  