Add Windows CI job

[disktnk]

• "onnxchainer.win.chainer-pre" job added
• On pytest 5, got Windows fatal exception" on onnx.checker.ValidationError`. I didn't detect the error but fixed using pytest<5

[disktnk]

/test

[pfn-ci-bot]

Successfully created a job for commit 163b52d:

• Dashboard for commit 163b52d

[codecov-io]

Codecov Report

Merging #220 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #220   +/-   ##
=======================================
  Coverage   89.99%   89.99%           
=======================================
  Files          24       24           
  Lines        1529     1529           
=======================================
  Hits         1376     1376           
  Misses        153      153

Impacted Files	Coverage Δ
onnx_chainer/functions/array.py	90.51% <100%> (ø)	⬆️
onnx_chainer/functions/math.py	85.71% <100%> (ø)	⬆️

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[shinh]

LGTM! (sorry for the large latency)