Make dist folder be created under right privileges

[webknjaz]

@asvetlov it's the same as for multidict.

Ref: aio-libs/multidict#117

[webknjaz]

I've decided to make script run atomic by moving dist dir creation there.

[codecov-io]

Codecov Report

Merging #2137 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2137   +/-   ##
=======================================
  Coverage   97.07%   97.07%           
=======================================
  Files          38       38           
  Lines        7728     7728           
  Branches     1347     1347           
=======================================
  Hits         7502     7502           
  Misses        102      102           
  Partials      124      124

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