Fix missing use-statement

Author: tvdijen

src/XML/ds/KeyInfo.php

@@ -7,6 +7,7 @@
 use DOMElement;
 use SimpleSAML\Assert\Assert;
 use SimpleSAML\XML\Exception\InvalidDOMElementException;
+use SimpleSAML\XML\Exception\SchemaViolationException;
 use SimpleSAML\XML\ExtendableElementTrait;
 use SimpleSAML\XML\SerializableElementInterface;
 use SimpleSAML\XML\XsNamespace as NS;