devops: separate wheels for OS/drivers

[mxschmitt]

Closes #117

Before:

(env) ➜  playwright-python git:(devops/publish-os-specific) du -sh dist/*
 89M    dist/playwright-0.0.4.post9+g875b380-py3-none-any.whl
 81M    dist/playwright-0.0.4.post9+g875b380.tar.gz

After:

(env) ➜  playwright-python git:(devops/publish-os-specific) ✗ du -sh dist/*          
 24M    dist/playwright-0.0.4.post9+g875b380.d20200801-py3-none-macosx_10_13_x86_64.whl
 26M    dist/playwright-0.0.4.post9+g875b380.d20200801-py3-none-manylinux1_x86_64.whl
 24M    dist/playwright-0.0.4.post9+g875b380.d20200801-py3-none-win_amd64.whl
300K    dist/playwright-0.0.4.post9+g875b380.d20200801.tar.gz

PIP will automatically in the end install the correct wheel since all were uploaded to the PyPi registry.

[coveralls]

Pull Request Test Coverage Report for Build 191536671

• 2 of 4 (50.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 88.439%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
playwright/main.py	2	4	50.0%

Totals
Change from base Build 191452784:	0.2%
Covered Lines:	3366
Relevant Lines:	3806

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💛 - Coveralls