Bump version to 2.19 for upcoming release

Author: pmeenan

www/common.inc

@@ -74,7 +74,7 @@ if (array_key_exists('HTTP_USER_AGENT', $_SERVER) &&
   $userIsBot = true;
 
 // constants
-define('VER_WEBPAGETEST', '2.18');   // webpagetest version
+define('VER_WEBPAGETEST', '2.19');   // webpagetest version
 define('VER_CSS', 68);           // version of the sitewide css file
 define('VER_JS', 32);            // version of the sitewide javascript file
 define('VER_JS_TEST', 30);       // version of the javascript specific to the test pages