Find the framework directory, lookup order
- specify framework path
- get framework name from
- use egg by default
@param {Object} options - options
@param  {String} options.baseDir - the current directory of application
@param  {String} [options.framework] - the directory of framework
@return {String} frameworkPath
function getFrameworkPath({ framework, baseDir }) {
  const pkgPath = path.join(baseDir, 'package.json');
  assert(fs.existsSync(pkgPath), `${pkgPath} should exist`);

  const moduleDir = path.join(baseDir, 'node_modules');
  const pkg = utility.readJSONSync(pkgPath);

  // 1. pass framework or customEgg
  if (framework) {
    // 1.1 framework is an absolute path
    // framework: path.join(baseDir, 'node_modules/${frameworkName}')
    if (path.isAbsolute(framework)) {
      assert(fs.existsSync(framework), `${framework} should exist`);
      return framework;
    }
    // 1.2 framework is a npm package that required by application
    // framework: 'frameworkName'
    return assertAndReturn(framework, moduleDir);
  }

  // 2. framework is not specified
  // 2.1 use framework name from pkg.egg.framework
  if (pkg.egg && pkg.egg.framework) {
    return assertAndReturn(pkg.egg.framework, moduleDir);
  }

  // 2.2 use egg by default
  return assertAndReturn('egg', moduleDir);
}