Ensure posix compliant joins for urls in middleware (facebook#11640)

Author: psiservices-justin-sullard

packages/react-dev-utils/noopServiceWorkerMiddleware.js

@@ -11,7 +11,7 @@ const path = require('path');
 
 module.exports = function createNoopServiceWorkerMiddleware(servedPath) {
   return function noopServiceWorkerMiddleware(req, res, next) {
-    if (req.url === path.join(servedPath, 'service-worker.js')) {
+    if (req.url === path.posix.join(servedPath, 'service-worker.js')) {
       res.setHeader('Content-Type', 'text/javascript');
       res.send(
         `// This service worker file is effectively a 'no-op' that will reset any

packages/react-dev-utils/redirectServedPathMiddleware.js

@@ -19,7 +19,7 @@ module.exports = function createRedirectServedPathMiddleware(servedPath) {
     ) {
       next();
     } else {
-      const newPath = path.join(servedPath, req.path !== '/' ? req.path : '');
+      const newPath = path.posix.join(servedPath, req.path !== '/' ? req.path : '');
       res.redirect(newPath);
     }
   };