completions: make uuid -n expect an argument (#643)

Before this commit, tab completion after `-n` would suggest global
options, even though `-n` without an argument is an error. For the fish
completions:

    $ configlet uuid -n[Tab]
    -nh  (Show help)  -nt  (Select a track directory)  -nv  (Verbose level)

This commit removes that completion for both the bash and fish
completion scripts.

The fish docs for `complete` [1] describe the relevant options as:

    -f or --no-files
    This completion may not be followed by a filename.

    -r or --require-parameter
    This completion must have an option argument, i.e. may not be followed by another option.

    -x or --exclusive
    Short for -r and -f.

[1] https://fishshell.com/docs/current/cmds/complete.html

Closes: #636

completions/configlet.bash

@@ -58,7 +58,14 @@ _configlet_complete_info_() {
 }
 
 _configlet_complete_uuid_() {
-  _configlet_complete_options_ "-n --num $global_opts"
+  case $prev in
+    '-n' | '--num')
+      return 0 # Don't suggest a global option if -n has no argument.
+      ;;
+    *)
+      _configlet_complete_options_ "-n --num $global_opts"
+      ;;
+  esac
 }
 
 _configlet_complete_fmt_() {

completions/configlet.fish

@@ -14,7 +14,7 @@ complete -c configlet -n "__fish_seen_subcommand_from info" -s o -l offline -f -
 
 # uuid subcommand
 complete -c configlet -n "__fish_use_subcommand" -a uuid -f -d "Output a UUID"
-complete -c configlet -n "__fish_seen_subcommand_from uuid" -s n -l num -f -d "How many UUIDs"
+complete -c configlet -n "__fish_seen_subcommand_from uuid" -s n -l num -x -d "How many UUIDs"
 
 # fmt subcommand
 complete -c configlet -n "__fish_use_subcommand" -a fmt -f -d "Format the exercise '.meta/config.json' files"