chore(code.angularjs.org): don't use trailing slashes, and don't set headers after response was sent

Author: Narretz

scripts/code.angularjs.org-firebase/firebase.json

@@ -1,6 +1,7 @@
 {
   "hosting": {
     "public": "public",
+    "trailingSlash": false,
     "redirects": [
       {
         "source": "/:version/docs",

scripts/code.angularjs.org-firebase/functions/index.js

@@ -78,6 +78,10 @@ function sendStoredFile(request, response) {
   }
 
   function sendErrorResponse(error) {
+    if (response.headersSent) {
+      return response;
+    }
+
     let code = 500;
     let message = `General error. Please try again later.
       If the error persists, please create an issue in the