Added license for SwipeBack

Added license for liuguangqiang/SwipeBack library which was mentioned as "Unknown License" earlier.

README.md

@@ -90,7 +90,7 @@ Name | License | Demo
 [Phoenix Pull-to-Refresh](https://github.com/Yalantis/Phoenix) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/Phoenix.gif" width="65%">
 [Pull-to-Refresh.Tours](https://github.com/Yalantis/Taurus) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/Taurus.gif" width="65%">
 [InboxLayout](https://github.com/zhaozhentao/InboxLayout) | [MIT](https://opensource.org/licenses/MIT) | <img src="/art/InboxLayout.gif" width="49%">
-[SwipeBack](https://github.com/liuguangqiang/SwipeBack) | UnKnown | <img src="/art/SwipeBack.gif" width="49%"> <img src="/art/SwipeBack2.gif" width="49%">
+[SwipeBack](https://github.com/liuguangqiang/SwipeBack) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/SwipeBack.gif" width="49%"> <img src="/art/SwipeBack2.gif" width="49%">
 [ArcLayout](https://github.com/ogaclejapan/ArcLayout) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/arclayout1.gif" width="49%">
 [Dragger](https://github.com/ppamorim/Dragger) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/Dragger.gif" width="100%">
 [PhysicsLayout](https://github.com/Jawnnypoo/PhysicsLayout) | [Apache License V2](https://www.apache.org/licenses/LICENSE-2.0) | <img src="/art/PhysicsLayout.gif" width="49%">