Publish new version

[pabzm]

We should publish a new version that includes the darkmode-compatible icon. Even if the classic skin might not be compatible with future versions of Roundcube, a lot of people might still use it for quite a while with the 1.6-releases. So unless it's a lot of work it would be nice to publish the fixes.

[pabzm]

@alecpl Could you do this? Or write down the necessary steps?

As far as I can see there is no documentation on how previous releases were built and published, so I would have to "reverse engineer" my way towards it, which could take quite some time, I'm afraid.

[alecpl]

1. Run bin/build.sh
2. Commit the changes (if any)
3. Tag a release

That should be all.