title: ZSH keeps breaking with `zsh: fork failed:`
body: <p>In the past few weeks (possibly since I upgraded to Sierra) I keep getting this weird issue in <strong>iTerm2</strong> using ZSH.</p>
  
  <p>Basically, at intermittent points during my regular workflow, commands will stop working properly with the error:</p>
  
  <pre><code>_run-with-bundler:5: fork failed: resource temporarily unavailable
  zsh: fork failed: resource temporarily unavailable
  </code></pre>
  
  <p>Does anybody know why this is happening, and how I can fix it?</p>