grep: unexpecter argument

[nikaiw]

As for #204 and #211, I would expect grep to continue working the same way they would without rtk.

Problem

A common pattern behind used by claude is the following :

Strings something|grep -E 'value1|value|value3'

Currently we get:

error: unexpected argument '-E' found

  tip: to pass '-E' as a value, use '-- -E'