Added markdown to the requirements.txt.
Added markdown to the requirements.txt.

vasyarv/xblock-poll,open-craft/xblock-poll,mckinseyacademy/xblock-poll,vasyarv/xblock-poll,vasyarv/xblock-poll,mckinseyacademy/xblock-poll,open-craft/xblock-poll,msaqib52/xblock-poll,open-craft/xblock-poll,msaqib52/xblock-poll,msaqib52/xblock-poll,vasyarv/xblock-poll,mckinseyacademy/xblock-poll