Deprecation warning due to invalid escape sequences in Python 3.8

[tirkarthi]

Depreaction warning due to invalid escape sequences in Python 3.7 . https://github.com/asottile/pyupgrade/ can be used to resolve the warnings.

find . -iname '*py' | grep -Ev 'setup|rdf4|tool' | xargs -P4 -I{} python3.8 -Wall -m py_compile {}
./unidiff/constants.py:61: DeprecationWarning: invalid escape sequence \s
  '(?P<source_filename>[^\t]+?)(?:\t(?P<source_timestamp>[\s0-9:\+-]+))?'
./unidiff/constants.py:62: DeprecationWarning: invalid escape sequence \s
  '(?: and (?P<target_filename>[^\t]+?)(?:\t(?P<target_timestamp>[\s0-9:\+-]+))?)? (differ|has changed)')