title: brew install cmake unable to find formula
body: <p>I am trying to install cmake on a new machine running MacOS Sierra 10.12.6 using homebrew:</p>
  
  <p><code>brew install cmake</code> </p>
  
  <p>results in </p>
  
  <p><code>Error: No available formula with the name "cmake" 
  ==&gt; Searching for a previously deleted formula (in the last month)...
  Error: No previously deleted formula found.
  ==&gt; Searching for similarly named formulae...
  Error: No similarly named formulae found.
  ==&gt; Searching taps...
  ==&gt; Searching taps on GitHub...
  Error: No formulae found in taps.</code></p>
  
  <p>Can I not install cmake using homebrew? </p>
  
  <p>Update:  I tested this on a new machine, and it just installed without issue.  I'm not sure what's going on with the current machine, but if it's index issue as indicated below, how do I go about fixing it?  I've already run <code>brew update</code>.</p>