Fix wrong const cmdPanel

[Enc3phale]

Q	A
Bug fix?	Y
New feature?	N
Automated tests included?	N
Related user documentation PR URL	N
Related developer documentation PR URL	N
Issues addressed (#s or URLs)	N
BC breaks?	N
Deprecations?	N

Description:

Undo and Redo buttons are set in the wrong panel due to an error in this const : const cmdPanel = pnm.getPanel('options');

With this correction, it's like https://github.com/artf/grapesjs-preset-newsletter

[Enc3phale]

In Newsletter undo & redo buttons are within commands panel: https://github.com/artf/grapesjs-preset-newsletter/blob/master/src/buttons.js#L40

[DRoet]

Ok I'll take a look once I release v0.1.16

[DRoet]

Have you tested this locally? this commit seems to break the undo/redo buttons on the latest version

[artf]

With the latest release this is not an issue anymore