If SharePoint hides the Script Code of a Gist, use this script

embedGistInSharePoint.js

document._write = document.write;

document.write = function(str){
    if (str.indexOf('<div id=\"gist-') != 0) {
        if(str.indexOf('https://gist.github.com/stylesheets/gist/embed.css') == -1) {
            // if you got this far it's not a github document.write call
            document._write(str);
        }
        return;
    }
    var id = /<div id=\"gist-(\d+)/.exec(str)[1];
    var script = document.querySelector('script[src="https://gist.github.com/' + id + '.js"]');
    var div = document.createElement('div');
    div.innerHTML = str;
    script.parentNode.insertBefore(div, script.nextElementSibling);
}