[gtk-doc] meson: initialize variable with the right type

[Ignacio Casal Quinteiro <icq src gnome org>]

commit a79d53d71eaf9508f2ef15dc8854fa2e082bcf3e
Author: Ignacio Casal Quinteiro <qignacio amazon com>
Date:   Wed Oct 3 11:28:33 2018 +0200

    meson: initialize variable with the right type
    
    Otherwise this will fail when the highlight params are empty
    and you try to join the list
    Tested on OSX
    
    Fixes: https://gitlab.gnome.org/GNOME/gtk-doc/issues/58

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 4b0fd75..c2155c0 100644
--- a/meson.build
+++ b/meson.build
@@ -62,7 +62,7 @@ if fop_prg.found()
 endif
 
 highlight_prg_path = ''
-highlight_prg_args = ''
+highlight_prg_args = []
 if source_highlight_prg.found()
   highlight_prg_path = join_paths(source_highlight_prg.path())
   highlight_prg_args = [