community/dvtm: upgrade to latest git, and get copymode working

Latest git revision of dvtm fixes a few problems. Besides that, dvtm's copymode requires a compatible editor and pager.

The editor needs to use stderr for its user interface, so it can continue working even when stdout is redirected. The readme mentions sandy (which I can't find in Alpine repos) and the author's own vis as compatible editors.

The pager needs to be able to open a file at a particular line when supplied with something like "+10". Busybox less will treat that "+10" as a filename..