Rule new-lines incorrect on Python 3

[bz2]

When the yamllint command is run using Python 3, the new-lines rule will always pass when set to 'unix' and always fail when set to 'dos'. This is because the builtin open() for Python 3 includes universal newline handling, so translates the line endings at file read time.

Steps to reproduce

$ echo ---^M > test.yaml
$ echo "---                 
rules:
 new-lines:
  type: dos
" > typedos.yaml
$ echo "---
rules:
 new-lines:
  type: unix
" > typeunix.yaml
$ python2 -m yamllint -c typeunix.yaml test.yaml
test.yaml
  1:4       error    wrong new line character: expected \n  (new-lines)

$ python2 -m yamllint -c typedos.yaml test.yaml
$ python3 -m yamllint -c typeunix.yaml test.yaml
$ python3 -m yamllint -c typedos.yaml test.yaml
test.yaml
  1:4       error    wrong new line character: expected \r\n  (new-lines)

Note behaviour is as expected on Python 2 but incorrect on Python 3.