Use FileUtils#setFileLastModified instead of File#setLastModified

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@957441 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/SignJar.java

@@ -435,7 +435,7 @@ public class SignJar extends AbstractJarSignerTask {
 
         // restore the lastModified attribute
         if (preserveLastModified) {
-            targetFile.setLastModified(lastModified);
+            FILE_UTILS.setFileLastModified(targetFile, lastModified);
         }
     }