forEach(callback) {
		let thisArg = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : undefined;

		let pairs = getHeaders$5(this);
		let i = 0;
		while (i < pairs.length) {
			var _pairs$i = pairs[i];
			const name = _pairs$i[0],
			      value = _pairs$i[1];

			callback.call(thisArg, value, name, this);
			pairs = getHeaders$5(this);
			i++;
		}
	}
Iterate over all headers

@param   Function  callback  Executed for each item with parameters (value, name, thisArg)
@param   Boolean   thisArg   `this` context for callback function
@return  Void