Fixed kebabCase method and tests

[jamesg1]

Closes #632

• [x] Running yarn lint does not trigger any linter errors
• [x] The test of the method you have fixed is passing
• [x] You have written a new skeleton method for someone else to work on!
• [x] You have written tests to accompany your skeleton method

[jamesg1]

Hey @BlakeGuilloud I've fixed that merge conflict, thanks!