Fix a small type in README

README.md

@@ -99,7 +99,7 @@ The *commons* module contains extensions to the library that not everyone may ne
 
 ```gradle
 dependencies {
-    compile 'com.afollestad.material-dialogs:commons:0.8.0.0@arr'
+    compile 'com.afollestad.material-dialogs:commons:0.8.0.0@aar'
 }
 ```