bootstrap.js

function makeBootstrappingLoader(scriptBody, clientAppUrl, isAsync) {
    var loadAsync = isAsync ? "s.async = true;\n" : "";
        return "<script type=\"text/javascript\">\n" +
        "var s = document.createElement(\"script\");\n" +
        "s.setAttribute(\"src\", \"" + clientAppUrl + "\");\n" +
        "document.body.insertBefore(s, null)\n"+
        loadAsync +
        "function loaded(e) {\n" +
            scriptBody + "\n" +
            "s.removeEventListener(\"load\", loaded, false);\n" +
        "}\n" +
        "s.addEventListener(\"load\", loaded);\n" +
        "</script>";
}

Change line 6 from body to head