update addCategory resolver

@@ -4,6 +4,12 @@ export default {
   Mutation: {
     addCategory: async (_, args) => {
       const { name } = args;
+      const newCategory = await prisma.category.create({
+        data: {
+          name,
+        },
+      });
+      return newCategory;
     },
   },
 };