Expand forget() example to include removing multiple keys at once

[u01jmg3]

• Code formatting copied from session.md. However, I realise $collection->all(); is no longer present which other collection examples use.

docs/session.md

Lines 223 to 227 in 696cad1

	// Forget a single key...
	$request->session()->forget('name');
	// Forget multiple keys...
	$request->session()->forget(['name', 'status']);