Add missing $readline Configuration private member.
Add missing $readline Configuration private member.

adetch/psysh,barryvdh/psysh,lvht/psysh,damiankloip/psysh,bobthecow/psysh,lvht/psysh,bobthecow/psysh,mubassirhayat/psysh,mubassirhayat/psysh,damiankloip/psysh,barryvdh/psysh,damiankloip/psysh,adetch/psysh