Code typo in Caching middleware example

[sebilasse]

There is a typo in Learn/Middleware Fundamentals in the
src/middleware/ValueCachingMiddleware.ts

It reads

export const ValueCachingMiddleware = factory(({ middleware: { defer, icache }}) => {
    get(key: string) { 
      // ...
    }
}

but it returns an object and should read

export const ValueCachingMiddleware = factory(({ middleware: { defer, icache }}) => ({
    get(key: string) { 
      // ...
    }
})

(missing brackets or return)