codios with speed 10 fails to clear screen

[rdenham]

Describe the bug
If you set a codios slide to speed 10, when you go to the next slide, the codios output
remains visible.

Steps to reproduce the bug
Steps used to install present:

1. pip install present

Steps to reproduce the behavior:

1. modify a codios example and set speed to 10. E.g.,

❯ git diff 
diff --git a/docs/gallery/back-to-school/codios/async.yml b/docs/gallery/back-to-school/codios/async.yml
index 10721e0..de42078 100644
--- a/docs/gallery/back-to-school/codios/async.yml
+++ b/docs/gallery/back-to-school/codios/async.yml
@@ -1,4 +1,4 @@
-speed: 8
+speed: 10
 lines:
 - prompt: $
   in: project creation using

Expected behavior
You would expect that moving to the next slide, the previous codio slide would no longer be visible.

Screenshots
end of codios slide:

following slide (artifacts of codios slide still present)

How it should look:

Environment

• OS: [ubuntu 18.04]
• Terminal emulator: [Konsole]
• Python version: [3.7.9]
• present version: [e.g. 0.6.0]