[Merge] ~calvinmwadime/ubuntu-release-upgrader:fix_invalid_escape_sequence into ubuntu-release-upgrader:ubuntu/main

[Calvin Mwadime Makokha]

@xypron, thanks. I have updated it.
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https://code.launchpad.net/~calvinmwadime/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/463497
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~calvinmwadime/ubuntu-release-upgrader:fix_invalid_escape_sequence into ubuntu-release-upgrader:ubuntu/main.