Update Dracula Themes

- Update submodules for zathura, gtk, and vim dracula themes
- Add submodule update command to justfile

README.org

@@ -9896,6 +9896,10 @@ stow-delete:
 # Remove and re-create softlinks from .dotfiles to home directory
 stow-recreate:
     stow -v -R .
+
+# Update git submodules from remotes
+submodule-update:
+    git submodule update --init --recursive --remote --progress
 #+END_SRC
 
 * Miscellaneous Scripts