Pin Vega to 5.29 until we've found a solution to the "null" data value in the map (caused by vega/vega#3926?)

Author: mherger

mkdocs.yml

@@ -54,7 +54,7 @@ plugins:
         - docs/players-and-controllers/firmware-versions.yaml
 
 extra_javascript:
-  - https://cdn.jsdelivr.net/npm/vega@5
+  - https://cdn.jsdelivr.net/npm/vega@5.29
   - https://cdn.jsdelivr.net/npm/vega-lite@5
   - https://cdn.jsdelivr.net/npm/vega-embed@6