luakit: update to 2.3.1

## [2.3.1]

### Added

- Added command `:userscripts-reload` to reload lua scripts.
- The tabgroup plugin is now included in luakit (:tabmenu).
- Allow configuration of shortcuts that should be passed through (https://github.com/luakit/luakit/pull/921).
- Added scalable SVG desktop icon version.

### Changed

- Allow functions to be bound to more than one key (https://github.com/luakit/luakit/issues/913).

### Fixed

- No more `gdk_keymap_get_default()` compiler warning.
- Fixed an issue where links were hinted, but then could be followed.
- Fixed the paging on the the bookmarks page.
- Fixed build on Solaris.
- Fixed relocation errors on Sparc64.
- Fixed proxymenu to show default entries when proxymenu file is not present.
- The command mode cursor is now drawn in the user-specified foreground color.

(nia)