title: Travis determine which files changed
body: <p>I have a Travis script that runs for every push.</p>
  
  <p>I need to determine which files were modified in this push.</p>
  
  <p>Currently, I have this:</p>
  
  <p><code>CHANGED_FILES=($(git diff --name-only HEAD HEAD~1))</code></p>
  
  <p>The problem is that sometimes a push can include more than one commits, and this only looks at the last commit.</p>
  
  <p>What is the expected way to solve this?</p>