Fix invalid escape sequence '\ ' warning

[hynek]

I didn't go thru the whole code base, this is just a warning that has been pestering me for a while. :)

[codecov[bot]]

Codecov Report

Merging #258 (2690ab0) into master (e343043) will increase coverage by 0.02%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #258      +/-   ##
==========================================
+ Coverage   97.99%   98.01%   +0.02%     
==========================================
  Files          27       27              
  Lines        4336     4336              
  Branches      748      748              
==========================================
+ Hits         4249     4250       +1     
  Misses         56       56              
+ Partials       31       30       -1     

Impacted Files	Coverage Δ
glom/matching.py	99.36% <ø> (ø)

... and 1 file with indirect coverage changes

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[mahmoud]

:100: