[vala] build: Add missing include of Makefile.common

[Rico Tzschichholz <ricotz src gnome org>]

commit b2f72e24a7704ef7f549dd921c51922e1a51a674
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sun Aug 20 13:10:09 2017 +0200

    build: Add missing include of Makefile.common

 valadoc/tests/Makefile.am |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/valadoc/tests/Makefile.am b/valadoc/tests/Makefile.am
index d68d402..e18e158 100644
--- a/valadoc/tests/Makefile.am
+++ b/valadoc/tests/Makefile.am
@@ -1,3 +1,5 @@
+include $(top_srcdir)/Makefile.common
+
 NULL =
 
 TESTS_ENVIRONMENT = EXEEXT=$(EXEEXT) PACKAGE_SUFFIX=$(PACKAGE_SUFFIX) TOPBUILDDIR=$(abs_top_builddir) 
TOPSRCDIR=$(abs_top_srcdir) $(srcdir)/testrunner.sh