class Rubocop::Cop::Style::Proc

would be more appropriate.
This cops checks for uses of Proc.new where Kernel#proc

def on_block(node) 

def on_block(node)
  # We're looking for
  # (block
  #   (send
  #     (const nil :Proc) :new)
  #   ...)
  block_method, = *node
  convention(block_method, :expression) if block_method == TARGET
end