Fix version compatability test

This commit fixes the version compatability test by updating the version
to reflect the current version in core.

Original commit: elastic/x-pack-elasticsearch@0bb6dbc1c3

elasticsearch/x-pack/shield/src/test/java/org/elasticsearch/shield/VersionCompatibilityTests.java

@@ -37,6 +37,6 @@ public class VersionCompatibilityTests extends ESTestCase {
          *
          */
         assertThat("Remove workaround in LicenseService class when es core supports merging cluster level custom metadata",
-                   Version.CURRENT.equals(Version.V_5_0_0_alpha3), is(true));
+                   Version.CURRENT.equals(Version.V_5_0_0), is(true));
     }
 }