Bump TypeScript template to 3.8 (#8713)

Author: braedongough

packages/cra-template-typescript/template.json

@@ -8,7 +8,7 @@
       "@types/react": "^16.9.0",
       "@types/react-dom": "^16.9.0",
       "@types/jest": "^24.0.0",
-      "typescript": "~3.7.2"
+      "typescript": "^3.8.0"
     }
   }
 }