Fixed Google Play badge in README.

README.md

@@ -8,7 +8,7 @@ You can download the latest sample APK from this repo here: https://github.com/a
 
 It's also on Google Play:
 
-<a href="https://play.google.com/store/apps/details?id=https://play.google.com/store/apps/details?id=com.afollestad.materialdialogssample">
+<a href="https://play.google.com/store/apps/details?id=com.afollestad.materialdialogssample">
   <img alt="Get it on Google Play"
        src="https://developer.android.com/images/brand/en_generic_rgb_wo_60.png" />
 </a>