Python 3.8 runtime support

[Amwam]

Description

Adds python38 as a runtime.

Mimicked #1762 as a guide for the changes.
The incompatable change was the use of escape and parse_qs from cgi.

I also had to limit the docutils package so it matches botocode. A new version released on December 4th 2019 (https://pypi.org/project/docutils/0.16b0.dev0/#description) was being installed, which then caused conflicts when trying to install botocore. Fixed in master

GitHub Issues

Resolves #1968

[coveralls]

Coverage increased (+0.2%) to 33.6% when pulling 261d0a4 on Amwam:feature/python38 into 746385d on Miserlou:master.

[Amwam]

Not sure why the coverage is reporting as being lower.

[Amwam]

It seems coveralls has a limit on the coverage version, as 5.0 as only recently been released. Pinning the version has fixed the coverage tests.

[Aulig]

Would be great if this got merged :)

[kimbriancanavan]

Zappa/zappa/core.py

Lines 285 to 290 in 261d0a4

	if self.runtime == 'python2.7':
	self.manylinux_wheel_file_suffix = 'cp27mu-manylinux1_x86_64.whl'
	elif self.runtime == 'python3.6':
	self.manylinux_wheel_file_suffix = 'cp36m-manylinux1_x86_64.whl'
	else:
	self.manylinux_wheel_file_suffix = 'cp37m-manylinux1_x86_64.whl'

Will need to add 'python3.8' runtime here to set the wheel suffix correctly 👍

[Amwam]

@kimbriancanavan Good spot, fixed. Thanks!

[khafatech]

Thanks for merging @mcrowson ! 🎉