Replace IllegalArgumentException with InvalidArgumentException

IllegalArgumentException doesn't exist in PHP

Signed-off-by: Lukas Reschke <lukas@statuscode.ch>

Author: LukasReschke

lib/Saml2/Response.php

@@ -426,7 +426,7 @@ public function getId()
     public function getAssertionId()
     {
         if (!$this->validateNumAssertions()) {
-            throw new IllegalArgumentException("SAML Response must contain 1 Assertion.");
+            throw new InvalidArgumentException("SAML Response must contain 1 Assertion.");
         }
         $assertionNodes = $this->_queryAssertion("");
         $id = null;