COMPMID-1639: Add GenerateProposals to the graph API

Change-Id: Icf813a0a87d4a07e180eafdb5fa916b2ea4028d2
diff --git a/arm_compute/graph/Types.h b/arm_compute/graph/Types.h
index b9589b7..ceee776 100644
--- a/arm_compute/graph/Types.h
+++ b/arm_compute/graph/Types.h
@@ -135,6 +135,7 @@
     EltwiseLayer,
     FlattenLayer,
     FullyConnectedLayer,
+    GenerateProposalsLayer,
     NormalizationLayer,
     NormalizePlanarYUVLayer,
     PadLayer,