Remove support for previous PD version

Author: shiraji

README.md

@@ -54,13 +54,7 @@ There are 3 behaviors for rebuilding project after generating PermissionsDispatc
 
 # Supported PermissionsDispatcher version
 
-* [2.1.3](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.1.3)
-* [2.2.0](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.2.0)
-* [2.2.1](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.2.1)
-* [2.3.0](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.3.0)
-* [2.3.1](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.3.1)
-* [2.3.2](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.3.2)
-* [2.4.0](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/2.4.0)
+* [3.1.0](https://github.com/hotchemi/PermissionsDispatcher/releases/tag/3.1.0)
 
 ## License