Install docfix

[tpltnt]

Hi there,

I adjusted the list of supported operating systems to the reality of 2017.

Cheers,
tpltnt

[codecov-io]

Codecov Report

Merging #419 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #419      +/-   ##
=========================================
- Coverage   88.02%     88%   -0.02%     
=========================================
  Files         146     146              
  Lines       27578   27578              
  Branches     3921    3921              
=========================================
- Hits        24276   24271       -5     
- Misses       2599    2601       +2     
- Partials      703     706       +3

Impacted Files	Coverage Δ
src/allmydata/util/dictutil.py	97.19% <0%> (-0.71%)	⬇️
src/allmydata/immutable/checker.py	87.94% <0%> (-0.52%)	⬇️
src/allmydata/web/status.py	83.05% <0%> (-0.12%)	⬇️
src/allmydata/immutable/upload.py	96.24% <0%> (-0.1%)	⬇️
src/allmydata/mutable/servermap.py	94.2% <0%> (+0.32%)	⬆️

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[warner]

Looks good.. thanks! I'll land a rebased form to simplify the commit history for a one-line patch.