function swapCase(subject) {
    var subjectString = coerceToString(subject);
    return subjectString.split('').reduce(swapAndConcat, '');
  }
Converts the uppercase alpha characters of `subject` to lowercase and lowercase
characters to uppercase.

@function swapCase
@static
@since 1.3.0
@memberOf Case
@param  {string} [subject=''] The string to swap the case.
@return {string}              Returns the converted string.
@example
v.swapCase('League of Shadows');
// => 'lEAGUE OF sHADOWS'

v.swapCase('2 Bees');
// => '2 bEES'