Comment typo fix

library/src/main/java/com/afollestad/materialdialogs/MaterialDialog.java

@@ -525,7 +525,7 @@ public class MaterialDialog extends DialogBase implements
         }
 
         if (isStacked) {
-            // Since isStacked is now true, invalidate the initial visibilityy states of the action button views
+            // Since isStacked is now true, invalidate the initial visibility states of the action button views
             positiveButton.setVisibility(mBuilder.positiveText != null ? View.VISIBLE : View.GONE);
             neutralButton.setVisibility(mBuilder.neutralText != null ? View.VISIBLE : View.GONE);
             negativeButton.setVisibility(mBuilder.negativeText != null ? View.VISIBLE : View.GONE);