fix(*): do not use polyfill when running on Node.js

src/SASjs.ts

@@ -2,7 +2,9 @@ import { isIEorEdgeOrOldFirefox } from "./utils/isIeOrEdge";
 import * as e6p from "es6-promise";
 (e6p as any).polyfill();
 if (isIEorEdgeOrOldFirefox()) {
-  window.fetch = undefined as any; // ensure the polyfill runs
+  if (window) {
+    window.fetch = undefined as any; // ensure the polyfill runs
+  }
 }
 // tslint:disable-next-line
 require("isomorphic-fetch");

src/utils/isIeOrEdge.ts

@@ -1,4 +1,7 @@
 export function isIEorEdgeOrOldFirefox() {
+  if (typeof window === "undefined") {
+    return false;
+  }
   const ua = window.navigator.userAgent;
 
   if (ua.indexOf("Firefox") > 0) {