Update proguard rules (#2447)

That was wrong class name

README.md

@@ -63,7 +63,7 @@ Depending on your ProGuard (DexGuard) config and usage, you may need to include
 
 ```pro
 -keep public class * implements com.bumptech.glide.module.GlideModule
--keep public class * extends com.bumptech.glide.AppGlideModule
+-keep public class * extends com.bumptech.glide.module.AppGlideModule
 -keep public enum com.bumptech.glide.load.resource.bitmap.ImageHeaderParser$** {
   **[] $VALUES;
   public *;
@@ -219,4 +219,4 @@ This is not an official Google product.
 [19]: https://github.com/wasabeef/glide-transformations
 [20]: http://bumptech.github.io/glide/
 [21]: http://bumptech.github.io/glide/doc/generatedapi.html
-[22]: https://muyangmin.github.io/glide-docs-cn/
+[22]: https://muyangmin.github.io/glide-docs-cn/