Fix DeprecationWarning in Python 3.6

[yan12125]

In Python 3.6, invalid escape sequences in string literals are deprecated: [1][2]

$ python3.6 -B -W error -c 'import appdirs'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
DeprecationWarning: invalid escape sequence '\D'

My patch fixes all of them.

[1] http://bugs.python.org/issue28128
[2] http://bugs.python.org/issue27364

[zoofood]

Thanks, this has been merged. My apologies for the delay, it was before I took up maintenance, and hadn't really examined the python 3.6 support closely enough. Cheers.

[yan12125]

Thanks!