vagrant up エラー：Vagrant failed to initialize at a very early stage:

vagrant upでエラー
vagrant のバージョンを変える
1. 最新版インストール
2. vagrant のバージョンを確認

vagrant upでエラー

$ vagrant up
Vagrant failed to initialize at a very early stage:

This Vagrant environment has specified that it requires the Vagrant
version to satisfy the following version requirements:
 >= 2.2.4

You are running Vagrant 2.1.5, which does not satisfy
these requirements. Please change your Vagrant version or update
the Vagrantfile to allow this Vagrant version. However, be warned
that if the Vagrantfile has specified another version, it probably has
good reason to do so, and changing that may cause the environment to
not function properly.

vagrant のバージョンを変えてください、とのこと。