chore: upgrade TypeScript to 4.1.5

We were blocked on doing this because API Extractor didn't support it,
but now it does, so we can bump TS and the API tooling in one go. None
of the breaking changes in TS4 cause us any issues.

package.json

@@ -69,8 +69,8 @@
   "devDependencies": {
     "@commitlint/cli": "^11.0.0",
     "@commitlint/config-conventional": "^11.0.0",
-    "@microsoft/api-documenter": "7.9.7",
-    "@microsoft/api-extractor": "7.10.4",
+    "@microsoft/api-documenter": "^7.12.7",
+    "@microsoft/api-extractor": "^7.13.1",
     "@types/debug": "0.0.31",
     "@types/mime": "^2.0.0",
     "@types/mocha": "^7.0.2",
@@ -107,7 +107,7 @@
     "standard-version": "^9.0.0",
     "text-diff": "^1.0.1",
     "ts-node": "^9.0.0",
-    "typescript": "3.9.5"
+    "typescript": "^4.1.5"
   },
   "husky": {
     "hooks": {

test/navigation.spec.ts

@@ -613,7 +613,7 @@ describe('navigation', function () {
           server.PREFIX + '/frames/one-frame.html'
         );
         const frame = await utils.waitEvent(page, 'frameattached');
-        await new Promise((fulfill) => {
+        await new Promise<void>((fulfill) => {
           page.on('framenavigated', (f) => {
             if (f === frame) fulfill();
           });