use proper app icon in documents provider

src/org/nextcloud/providers/cursors/RootCursor.java

@@ -53,7 +53,7 @@ public class RootCursor extends MatrixCursor {
                 .add(Root.COLUMN_DOCUMENT_ID, mainDir.getFileId())
                 .add(Root.COLUMN_SUMMARY, account.name)
                 .add(Root.COLUMN_TITLE, context.getString(R.string.app_name))
-                .add(Root.COLUMN_ICON, R.drawable.logo)
+                .add(Root.COLUMN_ICON, R.mipmap.ic_launcher)
                 .add(Root.COLUMN_FLAGS, Root.FLAG_SUPPORTS_SEARCH);
 
     }