Support enum flags of varying case

[childish-sambino]

Fixes

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Contributing to Twilio

All third party contributors acknowledge that any contributions they provide will be made under the same open source license that the open source project is provided under.

Short description of what this PR does:

• Accept varying case command API options and display the lower-case options in the help
• This is to support APIs that only accept a specific case, but don't call that out in their definition

If you have questions, please file a support ticket, or create a Github Issue in this repository.

[codecov]

Codecov Report

Merging #17 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #17   +/-   ##
=======================================
  Coverage   97.01%   97.01%           
=======================================
  Files          20       20           
  Lines         503      503           
=======================================
  Hits          488      488           
  Misses         15       15

Impacted Files	Coverage Δ
src/base-commands/twilio-api-command.js	92.04% <100%> (ø)	⬆️

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