Product info mutation (#14)

* Add mutation for product info

* Upgrade to apollo 3

src/resolvers/categories-resolver.ts

@@ -1,8 +1,7 @@
-import { IResolverObject } from 'graphql-tools';
 import { CategoryAPI } from '../datasources/category-api';
 import { ProductAPI } from '../datasources/product-api';
 
-const Category: IResolverObject = {
+const Category = {
   async products({ id }, _args, { dataSources }) {
     return (<ProductAPI>dataSources.productApi).getCategoryProducts(id);
   },