`mapjs-example/src/start.js`: When multiple mapjs on page, each control panel affects both maps

From v 4.2.3, when multiple maps enabled.

**Context**
Describe steps to reproduce the behavior:
1. `md2hf test/input/Example1_ClearlyFalse_WhiteSwan_simplified_2mapjs.md`
2. Select and edit node on each map.
3. Click undo.

Both nodes will undo.