functions.php

<?php


/**
 * Enqueue iOS bug fix
 *
 */
function be_enqueue_ios_bug_fix() {
	wp_enqueue_script( 'be-ios-bug', get_stylesheet_directory_uri() . '/lib/js/ios-bug.js' );
}
add_action( 'wp_enqueue_scripts', 'be_enqueue_ios_bug_fix' );

ios-bug.js

(function(doc) {

	var addEvent = 'addEventListener',
	    type = 'gesturestart',
	    qsa = 'querySelectorAll',
	    scales = [1, 1],
	    meta = qsa in doc ? doc[qsa]('meta[name=viewport]') : [];

	function fix() {
		meta.content = 'width=device-width,minimum-scale=' + scales[0] + ',maximum-scale=' + scales[1];
		doc.removeEventListener(type, fix, true);
	}

	if ((meta = meta[meta.length - 1]) && addEvent in doc) {
		fix();
		scales = [.25, 1.6];
		doc[addEvent](type, fix, true);
	}

}(document));