title: Why brew install returns "cask is unavailable" on terminal if homebrew's website shows a different information?
body: <p>I am trying to install this software called Next browser. There is a page about it on <a href="https://formulae.brew.sh/cask/next" rel="nofollow noreferrer">brew.sh</a>.</p>
  <p>When I run the command displayed on homebrew's webpage on my <strong>Ubuntu 18.04 LTS</strong> terminal:</p>
  <pre><code>$ brew install --cask next
  </code></pre>
  <p>I get the following error message:</p>
  <pre><code>Updating Homebrew...
  Error: Cask 'next' is unavailable: No Cask with this name exists.
  </code></pre>
  <p>Observation, I am able to sucessfully install other packages like:</p>
  <pre><code>brew install hello
  </code></pre>
  <p>Why is this happening?</p>
  <p>Is there a way to fix this?</p>