COMPMID-1639: Add GenerateProposals to the graph API

Change-Id: Icf813a0a87d4a07e180eafdb5fa916b2ea4028d2
diff --git a/arm_compute/graph/nodes/NodesFwd.h b/arm_compute/graph/nodes/NodesFwd.h
index e704557..929a402 100644
--- a/arm_compute/graph/nodes/NodesFwd.h
+++ b/arm_compute/graph/nodes/NodesFwd.h
@@ -43,6 +43,7 @@
 class EltwiseLayerNode;
 class FlattenLayerNode;
 class FullyConnectedLayerNode;
+class GenerateProposalsLayerNode;
 class InputNode;
 class NormalizationLayerNode;
 class NormalizePlanarYUVLayerNode;