Use File.exist? instead of File.exists?

File.exists? is deprecated in Ruby 2.1+.
Library/Formula/aubio.rb: update to 0.4.1
Library/Formula/aubio.rb: complete --without-python option
Library/Formula/aubio.rb: add ENV.refurbished_args, thanks to @mystydemeo
aubio: add 0.4.1 bottle.