Android SDK Tools and ADT plugin updated Revision 21.1.0
Android SDK Tools updated Revision 21.1.0, you can now update it in Eclipse by select Windows -> Android SDK Manager.
The SDK Tools r21.1.0 is designed for use with ADT 21.1.0 and later, to update ADT in Eclipse, select Help -> Check for updates.
Remark: if you cannot update ADT (No updates were found), double check the setting of your software site (in Help -> Install New Software...), make sure https://dl-ssl.google.com/android/eclipse/ is included. In my case, the default included site is http://dl-ssl.google.com/android/eclipse/, no updates were found at this moment!