Update pre-commit hook kynan/nbstripout to v0.8.1

Author: renovate[bot]

.pre-commit-config.yaml

@@ -28,7 +28,7 @@ repos:
 
     ## Nbstripout
   - repo: https://github.com/kynan/nbstripout
-    rev: 0.7.1
+    rev: 0.8.1
     hooks:
       - id: nbstripout