Enable `Lint/BooleanSymbol` cop
Enable `Lint/BooleanSymbol` cop

In fact, `Lint/BooleanSymbol` cop has not detected any offenses.
This commit will enable it for future reviews.

maxjacobson/rubocop,tejasbubane/rubocop,rrosenblum/rubocop,rrosenblum/rubocop,maxjacobson/rubocop,maxjacobson/rubocop,tejasbubane/rubocop,tejasbubane/rubocop,rrosenblum/rubocop