community/jj_tui: upgrade to 0.8.2

https://github.com/faldor20/jj_tui/compare/v0.7.4...v0.8.2

add `cd "$startdir"` to opam_lock() as running
`abuild unpack default_prepare opam_lock` changes
$PWD to $builddir, which causes `abuild checksum`
ran at the end of opam_lock() to fail