message: if package.json main field exists, convert file extension
diff: @@ -183,6 +183,8 @@ export function generatePackageJson(
  `so this package will not be directly importable by name. ` +
  `Manually update main in your bower.json or package.json to fix.`);
  }
  + } else {
  + packageJson.main = replaceHtmlExtensionIfFound(packageJson.main);
  }
  if (!packageJson.author &&
  