Wrong argument name in documentation

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Steps to reproduce the behavior:
1. See doc about exporting annotations https://labelstud.io/guide/export.html#Export-using-console-command
2. Run the command `label-studio export --path=`
3. Note the error "label-studio: error: unrecognized arguments: --path=..."

**Fix**
use `--export-path` instead of `--path`

This is also the argument name show by label-studio

**Additional context**
Add any other context about the problem here.