Fixes some typos in webhook section

This PR fixes the following typos:
### @debug.html:

- ammend --> amend
- . you --> . You

### @event.html

- messages's --> message's
- arugments --> arguments
- reponse --> response.

It also removes some white spaces that are not being used at the end of some lines of code. This doesn't affect the html result as `newline` turns into `white space` when inside a paragraph.

```html
<p>firstline
second
third</p>
```

generates
```
firstline second third
```