title: exclude files from triggering a travis ci build on github
body: <p>Our organization uses <code>travis-ci</code> within <code>github</code> for basic sanity checking when a change is committed. Is there a way to prevent a full travis build/run when changes to specific files or file types are made?</p>
  
  <p>As the simplest example:  if someone makes a change to the README.md file and wants to commit directly to master, we don't need to do a CI run before allowing this.</p>