Add autocomplete for --preserve in bash and zsh

auto-completion/bash/buku-completion.bash

@@ -62,6 +62,7 @@ _buku () {
         -i --import
         --immutable
         -n --count
+        --preserve
         -r --sreg
         --replace
         -s --sany

auto-completion/zsh/_buku

@@ -30,6 +30,7 @@ args=(
     '(--np)--np[noninteractive mode]'
     '(-o --open)'{-o,--open}'[open bookmarks in browser]'
     '(--oa)--oa[browse all search results immediately]'
+    '(--preserve)--preserve[preserve options]'
     '(-p --print)'{-p,--print}'[show bookmark details]'
     '(-r --sreg)'{-r,--sreg}'[match a regular exression]:regex'
     '(--replace)--replace[replace a tag]:tag to replace'