Issue jhedstrom#557: iWaitForAjaxToFinish fails

jQuery.active internal value may have negative value in some cases
causing inconsistent test results, as jquery supposedly increments the
value when an ajax request starts and decrements it when it finishes, it
should not influence the identification of active ajax requests

src/Drupal/DrupalExtension/Context/MinkContext.php

@@ -147,7 +147,7 @@ function isAjaxing(instance) {
       return (
         // Assert no AJAX request is running (via jQuery or Drupal) and no
         // animation is running.
-        (typeof jQuery === 'undefined' || jQuery.hasOwnProperty('active') === false || (jQuery.active === 0 && jQuery(':animated').length === 0)) &&
+        (typeof jQuery === 'undefined' || jQuery.hasOwnProperty('active') === false || (jQuery.active <= 0 && jQuery(':animated').length === 0)) &&
         d7_not_ajaxing && d8_not_ajaxing
       );
     }());