fix images path to graphic-design repo

[junghan0611]

change rules 1) live/spacemacs -> live/editors/spacemacs 2) images -> https://raw.githubusercontent.com/practicalli/graphic-design/live/editors/spacemacs/screenshots

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[practicalli-johnny]

Updating the images for the book is not as straight forward as changing the URL prefix. The new format for images is being used throughout the book as it is more reliable.

Also many of the images are being recreated with light and dark variants to work well with both book themes.

Such a large change should have been first raised as an issue, as mentioned in the contributing guide. Even without the above issues, it is unlikely such a large change would be accepted.

Thank you.