title: Git diff tool reset to git default
body: <p>I accidentally changed my git diff tool and it was not actually installed and I have no permissions over the machine. How can I revert to the original tool that shows changes in command line? It may sound silly but I have not been able to make a single diff and I have found no information about this, only on how to change it to others than the default. I have tried to unset the variable but it doesn't work.</p>