Update "tested up to" tag.

Author: dannyvankooten

readme.txt

@@ -3,7 +3,7 @@ Contributors: Ibericode, DvanKooten, hchouhan, lapzor
 Donate link: https://boxzillaplugin.com/#utm_source=wp-plugin-repo&utm_medium=boxzilla&utm_campaign=donate-link
 Tags: scroll triggered box, cta, social, pop-up, newsletter, call to action, mailchimp, contact form 7, social media, mc4wp, ibericode
 Requires at least: 3.8
-Tested up to: 4.5.2
+Tested up to: 4.5.3
 Stable tag: 3.0.3
 License: GPLv2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html