Remove left over directories in `img` directory
diff --git a/circle.yml b/circle.yml
index 5611ba0..bc5845d 100644
--- a/circle.yml
+++ b/circle.yml
@@ -137,6 +137,8 @@
       do
         convert $dir/$x/*.png -append $dir/$x.png
       done
+      # Remove all directories in $CIRCLE_ARTIFACTS/img
+      rm -R -- $dir/*/
 
     # finally, complain to Circle CI if there were nonzero test failures
     - |-