title: macOS Sierra 10.12 : Homebrew can't brew upgrade Warning: We do not provide support for this pre-release version
body: <p>Yesterday I upgrade macOS Sierra, When I brew upgade,appeared error:</p>
  
  <pre><code>     Warning: You are using OS X 10.12.
       We do not provide support for this pre-release version.
       You may encounter build failures or other breakages.
       Please create pull-requests instead of filing issues.
  </code></pre>
  
  <p>I search long time for solve for this problem ,</p>
  
  <p>eg:</p>
  
  <pre><code>sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
  </code></pre>
  
  <p>or:</p>
  
  <pre><code> sudo chown $(whoami):admin /usr/local &amp;&amp; sudo chown -R $(whoami):admin /usr/local
  </code></pre>
  
  <p>And then reboot OS,there are still this problem.</p>
  
  <blockquote>
    <p>/usr/local exists already, it can be writed.</p>
  </blockquote>
  
  <p>So,I don't  use brew upgrade, please help,I have a long time can't use it.</p>