function _setBooleanOption (key, val) {
  if (is.bool(val)) {
    this.options[key] = val;
  } else {
    throw is.invalidParameterError(key, 'boolean', val);
  }
}
Update a boolean attribute of the this.options Object.
@private
@param {string} key
@param {boolean} val
@throws {Error} Invalid key