title: Can't install php7 or php 7.1 with homebrew
body: <p>I was following a couple links that had this same sequence, namely <a href="https://daveismyname.blog/blog/installing-php-7-on-mac" rel="noreferrer">this example</a>. I was unable to get it done successfully. Here is the output from terminal</p>
  
  <pre><code>MacBook-Pro-4:/ SHennessy$ brew tap homebrew/dupes
  MacBook-Pro-4:/ SHennessy$ brew tap homebrew/versions
  MacBook-Pro-4:/ SHennessy$ brew tap homebrew/homebrew-php
  MacBook-Pro-4:/ SHennessy$ brew unlink php56
  Error: No such keg: /usr/local/Cellar/php56
  MacBook-Pro-4:/ SHennessy$ brew install php70
  ==&gt; Installing php70 from homebrew/php
  Error: You must `brew link libpng` before homebrew/php/php70 can be installed
  MacBook-Pro-4:/ SHennessy$ brew link php70
  Error: No such keg: /usr/local/Cellar/php70
  MacBook-Pro-4:/ SHennessy$
  </code></pre>
  
  <p>If anybody has any ideas that would be awesome, thanks in advance.</p>