Add typeRoots.

src/tsconfig.json

@@ -8,6 +8,9 @@
     "experimentalDecorators": true,
     "lib": [ "es2015", "dom" ],
     "noImplicitAny": false,
-    "suppressImplicitAnyIndexErrors": true
+    "suppressImplicitAnyIndexErrors": true,
+    "typeRoots": [
+        "../node_modules/@types"
+    ]
   }
 }