title: Is there a function to check if a package installed with devtools::install_github has been updated?
body: <p>I am the author of a package storred on github. My colleagues install this package with <code>devtools::install_github()</code>. They would like to test if the package has been updated or not. Is there a function to check that there has been a commit to the github master branch since they last installed the package?</p>