correct mistake in referencing constant

ugochimbo · ugochimbo · commit ee660bee4af3 · 2016-06-25T09:57:01.000Z
diff --git a/src/Paystack.php b/src/Paystack.php
@@ -170,7 +170,7 @@ public function isTransactionVerificationValid()
             case self::VS:
                 $validate = true;
                 break;
-            case self:ITF:
+            case self::ITF:
                 $validate = false;
                 break;
             default:
