Fixes (ignores) SSL certificate error on Windows

[tpberntsen]

Adds explicit ignoring of SSL certificate errors when downloading Chromium either when running the first time or through pyppeteer-install to avoid the following error (on Win x64):

SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1056)'))

[codecov-io]

Codecov Report

Merging #227 into dev will decrease coverage by 0.04%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##              dev     #227      +/-   ##
==========================================
- Coverage   92.38%   92.34%   -0.05%     
==========================================
  Files          48       48              
  Lines        7105     7105              
==========================================
- Hits         6564     6561       -3     
- Misses        541      544       +3

Impacted Files	Coverage Δ
pyppeteer/chromium_downloader.py	39.28% <0%> (ø)	⬆️
tests/test_frame.py	96.53% <0%> (-0.65%)	⬇️
pyppeteer/network_manager.py	92.1% <0%> (-0.27%)	⬇️
pyppeteer/execution_context.py	93.33% <0%> (+0.74%)	⬆️

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