function kebabCase(subject) {
    var subjectString = coerceToString(subject);

    if (subjectString === '') {
      return '';
    }

    return words(subjectString)
      .map(lowerCase)
      .join('-');
  }
Converts the `subject` to <a href="https://en.wikipedia.org/wiki/Letter_case#cite_ref-13">kebab case</a>,
also called <i>spinal case</i> or <i>lisp case</i>.

@function kebabCase
@static
@since 1.0.0
@memberOf Case
@param  {string} [subject=''] The string to convert to kebab case.
@return {string}              Returns the kebab case string.
@example
v.kebabCase('goodbye blue sky');
// => 'goodbye-blue-sky'

v.kebabCase('GoodbyeBlueSky');
// => 'goodbye-blue-sky'

v.kebabCase('-Goodbye-Blue-Sky-');
// => 'goodbye-blue-sky'