Fix import statement for XMLUnit 2 upgrade.

When the XMLUnit2 upgrade was done (commit: c39d3d1) this import was forgotten.

It causes the bug reported with XMLUnit1 (issue: #1193) to still be present when using `ResultMatchers#soapEnvelope(Source)`.

For more infos: #1193 (comment)

See #1370.
Related: #1193.

Author: AntoineJT

spring-ws-test/src/main/java/org/springframework/ws/test/server/ResponseMatchers.java

@@ -31,9 +31,9 @@
 import org.springframework.ws.WebServiceMessage;
 import org.springframework.ws.soap.SoapVersion;
 import org.springframework.ws.test.support.matcher.SchemaValidatingMatcher;
-import org.springframework.ws.test.support.matcher.SoapEnvelopeDiffMatcher;
 import org.springframework.ws.test.support.matcher.SoapHeaderMatcher;
 import org.springframework.ws.test.support.matcher.xmlunit2.PayloadDiffMatcher;
+import org.springframework.ws.test.support.matcher.xmlunit2.SoapEnvelopeDiffMatcher;
 import org.springframework.xml.transform.ResourceSource;
 
 /**