Merge pull request miragejs#2562 from ijlee2/patch-2559-for-windows

Patch miragejs#2559 for Windows

Author: SergeAstapov

packages/ember-cli-mirage/config/environment.js

@@ -1,5 +1,7 @@
 'use strict';
+
 const fs = require('fs');
+const path = require('path');
 
 function usingProxy() {
   const usingProxyArg = !!process.argv.filter(function (arg) {
@@ -11,7 +13,8 @@ function usingProxy() {
   }).length;
 
   let hasGeneratedProxies = false;
-  const proxiesDir = `${process.env.PWD}/server/proxies`;
+  const proxiesDir = path.join(process.cwd(), 'server', 'proxies');
+
   try {
     fs.lstatSync(proxiesDir);
     hasGeneratedProxies = true;