fix(secret-tool): protect unset opts[...] from pathname expansions

``unset opts["$word"]'' will be unintendedly expanded to `opts<X>'
when $word contains a character <X> and there is a file named
`opts<X>'.  Even if there is no matching filenames, when `shopt -s
failglob' is set, ``unset opts["$word"]'' always fails.  We should
quote it as "unset 'opts[$word]'".  In addition, it is better to
specify `-v' option in case that there is a confusing name of a shell
function.

Author: akinomyoga

completions/secret-tool

@@ -39,7 +39,7 @@ _secret_tool()
         search)
             local -A opts=([--all]="" [--unlock]="")
             for word in "${words[@]:2}"; do
-                [[ $word ]] && unset opts["$word"]
+                [[ $word ]] && unset -v 'opts[$word]'
             done
             COMPREPLY=($(compgen -W '${!opts[@]}' -- "$cur"))
             ;;