Add Support for Python 3.8

[duboviy]

No description provided.

[gyermolenko]

@duboviy
CI has failed.

Because it goes like this (and it is quite common practice among open-source projs):
travis -> tox testenv -> pytest

Your change fails because tox doesn't have corresponding env yet.
I think you could add env for 38 same as 37.

[duboviy]

@duboviy
CI has failed.

Because it goes like this (and it is quite common practice among open-source projs):
travis -> tox testenv -> pytest

Your change fails because tox doesn't have corresponding env yet.
I think you could add env for 38 same as 37.

Thanks a lot @gyermolenko ! I've tried it - works like a charm!

[codecov-io]

Codecov Report

Merging #306 into master will decrease coverage by 0.35%.
The diff coverage is n/a.

@@ Coverage Diff @@## master #306 +/- ## ========================================== - Coverage 32.82% 32.46% -0.36%  ========================================== Files 42 42 Lines 1496 1534 +38 ========================================== + Hits 491 498 +7 - Misses 1005 1036 +31

Impacted Files	Coverage Δ
patterns/structural/mvc.py	0% <0%> (ø)	⬆️
...atterns/behavioral/chain_of_responsibility__py2.py	0% <0%> (ø)	⬆️
patterns/other/blackboard__py3.py	0% <0%> (ø)	⬆️
patterns/behavioral/catalog.py	0% <0%> (ø)	⬆️
patterns/behavioral/memento.py	0% <0%> (ø)	⬆️
patterns/structural/flyweight__py2.py	0% <0%> (ø)	⬆️
patterns/behavioral/registry__py3.py	0% <0%> (ø)	⬆️
patterns/behavioral/registry__py2.py	0% <0%> (ø)	⬆️
patterns/other/blackboard__py2.py	0% <0%> (ø)	⬆️
...atterns/behavioral/chain_of_responsibility__py3.py	0% <0%> (ø)	⬆️
... and 4 more

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