Updated readme.txt for version 1.5.1.

Author: rfmeier

readme.txt

@@ -1,9 +1,9 @@
 === PHP Compatibility Checker ===
 Contributors: wpengine, octalmage, stevenkword, Taylor4484, pross, jcross
-Tags: php 7, php 5.5, php, version, compatibility, checker, wp engine, wpe, wpengine
-Requires at least: 3.5
-Tested up to: 5.2.2
-Stable tag: 1.5.0
+Tags: php 7, php, version, compatibility, checker, wp engine, wpe, wpengine
+Requires at least: 4.8
+Tested up to: 5.4
+Stable tag: 1.5.1
 License: GPLv2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html
 
@@ -113,6 +113,9 @@ To disclose security issues for this plugin please email [email protected]
 2. Compatibility results screen
 
 == Changelog ==
+= 1.5.1 =
+- Added Smart Plugin Manager to whitelisted plugins
+
 = 1.5.0 =
 - Added support for PHP 7.3 compatibility checks