[gtksourceview] docs: ignore regex private header

[Christian Hergert <chergert src gnome org>]

commit 2510db7264f853d78ec70aa2f0f66dfa5ae0adbe
Author: Christian Hergert <chergert redhat com>
Date:   Mon Nov 16 10:30:34 2020 -0800

    docs: ignore regex private header

 docs/reference/meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index b491ecc9..70e8d99f 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -57,6 +57,7 @@ reference_private_h = [
   'gtksourcecompletionwordsproposal-private.h',
   'gtksourcecompletionwordsutils-private.h',
   'gtksourcecompletionsnippetsproposal-private.h',
+  'implregex-private.h',
   'quarkset-inline.h',
 ]