Updated snipstart tag (#774)

Author: Evanthx

core/src/test/java/io/temporal/samples/nexus/caller/NexusServiceJunit5Test.java

@@ -19,7 +19,7 @@
 // cannot mock it. Since the SampleNexusService itself is mocked,
 // no handlers need to be set up or mocked.
 
-// @@@SNIPSTART java-nexus-service-sample-junit4-mock
+// @@@SNIPSTART java-nexus-service-sample-junit5-mock
 public class NexusServiceJunit5Test {
 
   private final SampleNexusService mockNexusService = mock(SampleNexusService.class);