Replace `true` with `false`

bool_literal_transformer.cr

require "compiler/crystal/syntax/*"

code = <<-CODE
def hello
  true
end
CODE

ast = Crystal::Parser.parse(code)

class BooleanTransformer < Crystal::Transformer
  def transform(node : Crystal::BoolLiteral)
    Crystal::BoolLiteral.new(false)
  end
end

puts ast.transform(BooleanTransformer.new)
# => will print:
# def hello
#   false
# end