CMD+Z retrieves state from other editor

[hirshbergshachar]

Hi,

When working on 2 scripts one after the other (re-loading the editor with different content), hitting CTRL+Z in the second script may overwrite it and replace the contents with the ones of the previous script.

To Reproduce:

1. Edit a script
2. Go to another script
3. Hit ctrl+z
4. The content of the script is overwritten with the content of the previous one

Video for illustration:

Brace version - 0.11.1