fix(mdtool): use -f -X '!pat' instead of -G pat

#1297 (comment)

The compgen option `-X '!pat'` has a problem that it only generates
the filenames in the current directory and that it does not perform
the filtering by the "cur" specified to the argument of `compgen`:

    $ compgen -G '*.md' -- doc/
    CHANGELOG.md
    CONTRIBUTING.md
    README.md
    style.md

In this patch, we use `-f -X '!pat'`, which does not have those
limitations.

Author: akinomyoga

completions/mdtool

@@ -21,18 +21,18 @@ _comp_cmd_mdtool()
                 #if [[ "$prev" == *: ]]; then
                 #   case $prev in
                 #       @(--p:|--project:))
-                #           _comp_compgen -- -G "*.mdp"
+                #           _comp_compgen -- -f -X '!*.mdp'
                 #           ;;
                 #       @(--f:|--buildfile:))
-                #           _comp_compgen -- -G "*.md[ps]"
+                #           _comp_compgen -- -f -X '!*.md[ps]'
                 #           ;;
                 #   esac
                 #fi
                 return
                 ;;
             "generate-makefiles")
                 compopt -o filenames
-                _comp_compgen -- -o filenames -G"*.mds"
+                _comp_compgen -- -o filenames -f -X '!*.mds'
                 if [[ $prev == *mds ]]; then
                     _comp_compgen -- -W '--simple-makefiles --s --d:'
                 fi