Add getDueDate method for Jira_Issue

Author: dvdvdmt

Jira/Issue.php

@@ -296,6 +296,18 @@ public function getWatchers()
         }
     }
 
+    /**
+     * get due date
+     *
+     * @return mixed
+     */
+    public function getDueDate()
+    {
+        if (isset($this->fields['Due Date'])) {
+            return $this->fields['Due Date'];
+        }
+    }
+
     /**
      * get information represented in call output due to expand=... suffix
      * @see https://docs.atlassian.com/jira/REST/latest/