updated python version to 3.9

Updated versioning of dsalgo module to support python 3.9

Fixes #80

Python versions are keep updating, hence module needs to be updated too.

[ *] I read the CONTRIBUTING document before making this pull request
[ *] My code follows the style guidelines of this project
[* ] I have performed a self-review of my own code or materials
[ *] I have commented my code or provided relevant documentation, particularly in hard-to-understand areas
[ ] My change requires change to documentation
[ ] I have updated documentation accordingly
[ ] I have updated the requirements file
[* ] My changes generate no new warnings
[ ] My PR currently breaks something (fix or feature that would cause existing functionality to not work as expected)
[ ] I have added tests to cover my changes
[ *] All new and existing tests passed.

codesankalp / dsalgo