we should do as we say, use ant:current in antlib descriptor

https://bz.apache.org/bugzilla/show_bug.cgi?id=65315

NOTICE

@@ -1,5 +1,5 @@
 Apache AntUnit
-Copyright 2005-2018 The Apache Software Foundation
+Copyright 2005-2018,2021 The Apache Software Foundation
 
 This product includes software developed at
 The Apache Software Foundation (https://www.apache.org/).

changes.xml

@@ -38,6 +38,11 @@
   </properties>
 
   <release version="1.5" date="unreleased">
+    <action type="fix" issue="65315">
+      We didn't follow our own best practice and hard-coded the
+      AntUnit URI inside the Antlib descriptor instead of using
+      ant:current.
+    </action>
   </release>
   <release version="1.4" date="2018-06-25">
     <action type="update" breaks-bwc="true">

src/main/org/apache/ant/antunit/antlib.xml

@@ -17,7 +17,7 @@ KIND, either express or implied.  See the License for the
 specific language governing permissions and limitations
 under the License.
 -->
-<antlib xmlns:au="antlib:org.apache.ant.antunit">
+<antlib xmlns:au="ant:current">
   <taskdef name="antunit"
     classname="org.apache.ant.antunit.AntUnit"/>