(docs): Update code snippet to match example

[emibloque]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[x] Other... Please describe: **Documentation update**.

What is the current behavior?

The Middleware documentation for Routing Matching is the same as in Controllers, but the code example isn't the same.

What is the new behavior?

It is easier to understand the example and the behaviour of the asterisk in route matching.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

[kamilmysliwiec]

Thanks!