[goffice] Docs: point to sources differently.

[Morten Welinder <mortenw src gnome org>]

commit 70d93c71a47a200240007f36a4ba621e688ebde3
Author: Morten Welinder <terra gnome org>
Date:   Wed Aug 12 19:21:08 2020 -0400

    Docs: point to sources differently.

 docs/reference/Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/docs/reference/Makefile.am b/docs/reference/Makefile.am
index 3d3099bc..3278839c 100644
--- a/docs/reference/Makefile.am
+++ b/docs/reference/Makefile.am
@@ -6,7 +6,7 @@ DOC_MODULE=goffice-@GOFFICE_API_VER@
 
 DOC_MAIN_SGML_FILE=goffice-docs.xml
 
-DOC_SOURCE_DIR=../../goffice
+DOC_SOURCE_DIR=$(top_srcdir)/goffice
 
 SCANGOBJ_OPTIONS=