.coveragerc: use a single source, but includes

[blueyed]

This makes it easier for Codecov to parse it.

[codecov-io]

Codecov Report

Merging #532 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #532      +/-   ##
=========================================
+ Coverage   85.55%   85.6%   +0.05%     
=========================================
  Files          32      33       +1     
  Lines        1620    1626       +6     
  Branches      140     140              
=========================================
+ Hits         1386    1392       +6     
  Misses        178     178              
  Partials       56      56

Flag	Coverage Δ
#dj110	81.85% <ø> (+0.06%)	⬆️
#dj111	83.33% <ø> (-0.19%)	⬇️
#dj18	80.56% <ø> (+0.07%)	⬆️
#dj19	80.13% <ø> (+0.07%)	⬆️
#dj20	79.02% <ø> (-0.17%)	⬇️
#djmaster	79.02% <ø> (-0.17%)	⬇️
#mysql_innodb	78.9% <ø> (-0.17%)	⬇️
#mysql_myisam	78.84% <ø> (-0.17%)	⬇️
#postgres	81.61% <ø> (+0.06%)	⬆️
#py27	83.27% <ø> (+0.06%)	⬆️
#py34	81.18% <ø> (+0.06%)	⬆️
#py35	79.02% <ø> (-0.17%)	⬇️
#py36	81.3% <ø> (+0.06%)	⬆️
#pypy	80.44% <ø> (+0.07%)	⬆️
#pypy3	79.64% <ø> (+0.07%)	⬆️
#pytest3	85.6% <ø> (+0.05%)	⬆️
#sqlite_file	80.44% <ø> (+0.07%)	⬆️

Impacted Files	Coverage Δ
pytest_django/compat.py	100% <0%> (ø)

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