Update overview.mdx

just to align naming `builder` and `build` 

like in
- https://redux-toolkit.js.org/rtk-query/usage/queries
- https://redux-toolkit.js.org/rtk-query/usage/mutations

Author: flexbox

docs/rtk-query/api/created-api/overview.mdx

@@ -26,7 +26,7 @@ For maintainability purposes, you may wish to split up endpoint definitions acro
 ```ts title="API Slice Contents" no-transpile
 const api = createApi({
   baseQuery: fetchBaseQuery({ baseUrl: '/' }),
-  endpoints: (builder) => ({
+  endpoints: (build) => ({
     // ...
   }),
 })