function createCaseFirst(methodName) {
  return function(string) {
    string = toString(string);

    var strSymbols = hasUnicode(string)
      ? stringToArray(string)
      : undefined;

    var chr = strSymbols
      ? strSymbols[0]
      : string.charAt(0);

    var trailing = strSymbols
      ? castSlice(strSymbols, 1).join('')
      : string.slice(1);

    return chr[methodName]() + trailing;
  };
}
Creates a function like `_.lowerFirst`.

@private
@param {string} methodName The name of the `String` case method to use.
@returns {Function} Returns the new case function.