replaced deprecated getActiveInstance() with get()

core/src/main/java/hudson/PluginWrapper.java

@@ -1236,7 +1236,7 @@ public class PluginWrapper implements Comparable<PluginWrapper>, ModelObject {
 
     @RequirePOST
     public HttpResponse doDoUninstall() throws IOException {
-        Jenkins jenkins = Jenkins.getActiveInstance();
+        Jenkins jenkins = Jenkins.get();
         
         jenkins.checkPermission(Jenkins.ADMINISTER);
         archive.delete();