brew upgrade <package> does not update to the latest version
<p>I've noticed this happening a few times but this most recent instance is with <code>wp-cli</code> Running <code>brew upgrade wp-cli</code> does not download the latest version.</p>

<pre><code>$ brew upgrade wp-cli
Error: homebrew/php/wp-cli 0.20.1 already installed

$ brew info wp-cli
homebrew/php/wp-cli: stable 0.20.1, HEAD
A set of command-line tools for managing WordPress installations.
http://wp-cli.org/
/usr/local/Cellar/wp-cli/0.20.1 (2635 files, 15M) *
  Built from source
From: https://github.com/Homebrew/homebrew-php/blob/master/Formula/wp-cli.rb
</code></pre>

<p>Note the version is <code>0.20.1</code>. When I check <a href="https://github.com/Homebrew/homebrew-php/blob/master/Formula/wp-cli.rb#L10" rel="noreferrer">the formula repo</a>, I see,</p>

<pre><code>head "https://github.com/wp-cli/wp-cli.git"
</code></pre>

<p>When I check <a href="https://github.com/wp-cli/wp-cli" rel="noreferrer">that repo</a>, I see that the version in the master branch is <a href="https://github.com/wp-cli/wp-cli/blob/master/VERSION" rel="noreferrer">0.24.0</a>. <code>brew info</code> and <code>wp --version</code> both return <code>0.20.1</code>. Why isnt Homebrew grabbing the latest version? How do I force it to get the latest?</p>