composer 提示php版本过高

执行composer install遇到错误：Your requirements could not be resolved to an installable set of packages. 这是因为不匹配composer.json要求的版本

完整错误如下：

vagrant@homestead:/usr/share/nginx/html/laravel-blog$ sudocomposerinstall
Loadingcomposerrepositorieswithpackage information
Installingdependencies (includingrequire-dev) fromlockfile
Yourrequirementscouldnot beresolvedto aninstallablesetofpackages.
 
  Problem 1
    - Installationrequestfor doctrine/instantiator 1.0.3 -> satisfiablebydoctrine/instantiator[1.0.3].
    - doctrine/instantiator 1.0.3 requiresphp ~5.3 -> yourPHPversion (7.0.3) doesnot satisfythatrequirement.
  Problem 2
    - doctrine/instantiator 1.0.3 requiresphp ~5.3 -> yourPHPversion (7.0.3) doesnot satisfythatrequirement.
    - phpunit/phpunit-mock-objects 2.3.0 requiresdoctrine/instantiator ~1.0,>=1.0.1 -> satisfiablebydoctrine/instantiator[1.0.3].
    - Installationrequestfor phpunit/phpunit-mock-objects 2.3.0 -> satisfiablebyphpunit/phpunit-mock-objects[2.3.0].

提示我的PHP 7版本太高，不符合composer.json需要的版本，但是在PHP 7下应该也是可以运行的，composer可以设置忽略版本匹配，命令是：

composer install --ignore-platform-reqs

composer update --ignore-platform-reqs