[vala/0.42] doc: Fix build of internal-api-docs

[Rico Tzschichholz <ricotz src gnome org>]

commit f0d94a2bb408cfabdcbda970a91aaafbae5da278
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Mon Oct 29 16:39:29 2018 +0100

    doc: Fix build of internal-api-docs

 doc/Makefile.am | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 758ad733a..90368ff28 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -100,6 +100,7 @@ internal-apis/ccode: $(ccode_VALASOURCES) internal-apis/gee
                --package-name ccode \
                --package-version $(PACKAGE_VERSION) \
                --vapidir=$(top_builddir)/gee --pkg gee \
+               --vapidir=$(top_builddir)/vala --pkg vala \
                $(filter %.vala,$^)
        @touch $@