fix(propositional_logic.rst): fixes from Kevin Sullivan
fix(propositional_logic.rst): fixes from Kevin Sullivan

leanprover/logic_and_proof,avigad/logic_and_proof,fpvandoorn/logic_and_proof,rlewis1988/logic_and_proof,leanprover/logic_and_proof,fpvandoorn/logic_and_proof,avigad/logic_and_proof,rlewis1988/logic_and_proof,leanprover/logic_and_proof,fpvandoorn/logic_and_proof,rlewis1988/logic_and_proof,avigad/logic_and_proof