use local variable instead of module.exports in example

Co-authored-by: Esben Sparre Andreasen <esbena@github.com>

javascript/ql/src/semmle/javascript/frameworks/NodeJSLib.qll

@@ -480,7 +480,7 @@ module NodeJSLib {
         )
         or
         // const fs = require('fs');
-        // module.exports = methods.reduce((obj, method) => {
+        // let fs_copy = methods.reduce((obj, method) => {
         //  obj[method] = fs[method];
         //  return obj;
         // }, {});