COMPMID-417: Include std::vector where needed.

Change-Id: I8a0c88b3c37a3d82f14493fa0b51108b3bdac852
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/79407
Reviewed-by: Moritz Pflanzer <moritz.pflanzer@arm.com>
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
diff --git a/tests/validation/ReferenceCPP.h b/tests/validation/ReferenceCPP.h
index 9debdee..e7567ae 100644
--- a/tests/validation/ReferenceCPP.h
+++ b/tests/validation/ReferenceCPP.h
@@ -29,6 +29,7 @@
 #include "RawTensor.h"
 
 #include <ostream>
+#include <vector>
 
 namespace arm_compute
 {