Update moquette-broker coordinates to resolve the 401 unauthorized error from Jitpack

[dskarzh]

This PR corrects instructions in README.md on how to embed moquette in other projects

[andsel]

Left a comment to know your opinion on the version name v0.18.0 vs 0.18.0

[andsel]

Ahh it's the tag name and Moquette always used vM.M.P format. I think it's ugly to use

<version>v0.18.0</version>

If you also feel the same, I think I should switch tag policy to remove the v from the tag.
In past I used that to distinguish tags from version branches.

Let me know what do you think

[dskarzh]

I completely agree that the v prefix is not only ugly but also unusual in the Java ecosystem.

[andsel]

Created tag 0.18.0 https://github.com/moquette-io/moquette/tree/0.18.0 so you could drop the v from the version tag.

[dskarzh]

Thanks. That works, though group ID still missing .moquette. I updated the PR to omit v prefix.

[andsel]

LGTM

[andsel]

Thanks @dskarzh for your contribution!