#75: add missing import

Author: miszobi

core/src/test/java/com/onelogin/saml2/test/util/UtilsTest.java

@@ -32,6 +32,7 @@
 import java.security.PrivateKey;
 import java.security.SignatureException;
 import java.security.spec.InvalidKeySpecException;
+import java.util.Collections;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.Map;