Add Service-Worker header to checkValidServiceWorker (#6753)

* Add header to checkValidServiceWorker (ts)

* Add header to checkValidServiceWorker

Author: darthmaim

packages/react-scripts/template-typescript/src/serviceWorker.ts

@@ -108,7 +108,9 @@ function registerValidSW(swUrl: string, config?: Config) {
 
 function checkValidServiceWorker(swUrl: string, config?: Config) {
   // Check if the service worker can be found. If it can't reload the page.
-  fetch(swUrl)
+  fetch(swUrl, {
+    headers: { 'Service-Worker': 'script' }
+  })
     .then(response => {
       // Ensure service worker exists, and that we really are getting a JS file.
       const contentType = response.headers.get('content-type');

packages/react-scripts/template/src/serviceWorker.js

@@ -100,7 +100,9 @@ function registerValidSW(swUrl, config) {
 
 function checkValidServiceWorker(swUrl, config) {
   // Check if the service worker can be found. If it can't reload the page.
-  fetch(swUrl)
+  fetch(swUrl, {
+    headers: { 'Service-Worker': 'script' }
+  })
     .then(response => {
       // Ensure service worker exists, and that we really are getting a JS file.
       const contentType = response.headers.get('content-type');