title: Npm said I don't have yarn, but I already installed with Npm
body: <p>I am doing my nestjs project.
  I recently setup my new macbook pro.</p>
  <p>I have Node, Npm, and Yarn installed.
  But when I tried to install class-validator and class-transformer package with Npm,
  I got a error message :</p>
  <p>Unsupported engine. required: { node: '&gt;= 10.13.0', npm: '^6.11.0', yarn: '&gt;= 1.13.0' }, current: { node: 'v15.11.0', npm: '7.6.0' }</p>
  <p>But when I type npm -g ls, or yarn --version, yarn is there.
  How should I fix it?</p>
  <p>Thanks.</p>