Koa Middleware example: should not catch `await next()`
Hello!

On this wiki page https://github.com/animir/node-rate-limiter-flexible/wiki/Koa-Middleware

```js
app.use(async (ctx, next) => {
  try {
    await rateLimiter.consume(ctx.ip)
    await next()
  } catch (rejRes) {
    ctx.status = 429
    ctx.body = 'Too Many Requests'
    // Or you can throw an exception
    // ctx.throw(429, 'Too Many Requests')
  }
})
```

I believe we should not try/catch `await next()`. Only the `rateLimiter.consume`.
If the next chain of middlewares do throw, and this middleware catch it, Koa will return a `429 Too Many Requests`.

I think it may be very confusing for beginners which use this snippet and may not understand why is so.

Therefore, I propose to edit the wiki page with the following:

```js
app.use(async (ctx, next) => {
  try {
    await rateLimiter.consume(ctx.ip)
  } catch (rejRes) {
    ctx.status = 429
    ctx.body = 'Too Many Requests'
    // Or you can throw an exception
    // ctx.throw(429, 'Too Many Requests')
    return;
  }

  await next()
})
```

<details>
  <summary>I tested this behaviors with the following snippet.</summary>
  
```js
const Koa = require('koa');

const app = new Koa();

app.use(async (ctx, next) => {
  try {
    await next();
  }
  catch {
    ctx.body = 'catched';
  }
});

app.use(async ctx => {
  throw 'middleware2';
})

app.listen(3001);
```

I effectively get answer `catched`.
</details>