Add flake8 quality checks to .travis.yml

[czgdp1807]

Description of the problem

Example of the problem

References/Other comments

[hpnightowl]

can i take this issue as the part of swoc and add github action instead of travis.yml ? both works same btw

[czgdp1807]

Sure. Make separate PRs for migrating to Github action and adding flake8 checks.

[hpnightowl]

can you as this task with SWOC tag? i am doing pr

[hpnightowl]

@czgdp1807 for which python package version should i go? i have make for all 3 version like 3.7 3.8 3.9 https://github.com/hpnightowl/pydatastructs/commit/d0ac9135bab07392d416b46c468f0483aa5c3f1a

[czgdp1807]

I think anything greater than 3.5 should work(or whatever is there in the travis.yml).

[czgdp1807]

I will label your PR with the appropriate labels.