create monoalphabetic cipher

[radadiyamohit81]

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[TravisBuddy]

Travis tests have failed

Hey @radadiyamohit81,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

TravisBuddy Request Identifier: 2023a820-1083-11eb-af89-615b230ba186

[cclauss]

Can you please do python3 -m pip install flake8 on your local computer and then.

flake8 mono_alphabetic_ciphers.py

[radadiyamohit81]

let me try it

[radadiyamohit81]

Thank you @cclauss, I learned new things from this Thank you so much

[cclauss]

One last change needed...
charsA, charsB, symIndex, myMessage, myKey, myMode -->
chars_a, chars_b, sym_index, message, key, mode

[cclauss]

Cool... I would have simplified with from string import ascii_letters but this way works too.

[radadiyamohit81]

Ya its works too and Thank you so much