Fix Lintian warning: manpage-has-bad-whatis-entry

This patch fixes the problem where lexgrog fails to parse the NAME section
when the provided command contains space, e.g. "rootcmd subcmd".

Explanation from Lintian:

 Each manual page should start with a "NAME" section, which lists the
 name and a brief description of the page separated by "\-".  The "NAME"
 section is parsed by lexgrog and used to generate a database that's
 queried by commands like apropos and whatis.  This tag indicates that
 lexgrog was unable to parse the NAME section of this manual page.

 For manual pages that document multiple programs, functions, files, or
 other things, the part before "\-" should list each separated by a comma
 and a space.  Each thing listed must not contain spaces; a man page for a
 two-part command like "fs listacl" must use something like "fs_listacl"
 in the "NAME" section so that it can be parsed by lexgrog.

Ref: lexgrog(1), groff_man(7), groff_mdoc(7)

man_docs.go

@@ -111,12 +111,13 @@ func fillHeader(header *GenManHeader, name string) {
 }
 
 func manPreamble(out *bytes.Buffer, header *GenManHeader, name, short, long string) {
+	dashName := strings.Replace(name, " ", "-", -1)
 	fmt.Fprintf(out, `%% %s(%s)%s
 %% %s
 %% %s
 # NAME
 `, header.Title, header.Section, header.date, header.Source, header.Manual)
-	fmt.Fprintf(out, "%s \\- %s\n\n", name, short)
+	fmt.Fprintf(out, "%s \\- %s\n\n", dashName, short)
 	fmt.Fprintf(out, "# SYNOPSIS\n")
 	fmt.Fprintf(out, "**%s** [OPTIONS]\n\n", name)
 	fmt.Fprintf(out, "# DESCRIPTION\n")