desktop/buku: Use systemwide dir for bash completion files

desktop/buku/buku.SlackBuild

@@ -84,7 +84,7 @@ python3 setup.py build
 python3 setup.py install --root=$PKG --prefix=/usr --optimize=1
 
 install -Dm644 auto-completion/fish/buku.fish $PKG/usr/share/fish/vendor_completions.d/buku.fish
-install -Dm644 auto-completion/bash/buku-completion.bash $PKG/etc/bash_completion.d/buku
+install -Dm644 auto-completion/bash/buku-completion.bash $PKG/usr/share/bash-completion/completions/buku
 install -Dm644 auto-completion/zsh/_buku $PKG/usr/share/zsh/site-functions/_buku
 
 find $PKG -print0 | xargs -0 file | grep -e "executable" -e "shared object" | grep ELF \