fix whitespace in source.list

[amauf]

https://tickets.puppetlabs.com/browse/MODULES-2889

[daenney]

Thanks for the contribution, I'd be happy to merge this once:

• All commits are squashed into one
• The commit message is rewritten. Since there exists a ticket for this issue it should include that. See commit 9f43b2d as an example

[tphoney]

Looks good, once we get the squash 👍

[amauf]

Squashed and added ticket id in commit messages. :)