bump up onnx version (#8975)

Summary:
To include the change in https://github.com/onnx/onnx/pull/1151
Closes https://github.com/pytorch/pytorch/pull/8975

Reviewed By: bddppq

Differential Revision: D8673552

Pulled By: yinghai

fbshipit-source-id: f55c270ef869bd2e19fdabbdf906a6ae12129791
diff --git a/third_party/onnx b/third_party/onnx
index 458c521..7537916 160000
--- a/third_party/onnx
+++ b/third_party/onnx
@@ -1 +1 @@
-Subproject commit 458c5218446591e610614f04190a68e475840e23
+Subproject commit 7537916872738fd47c12cebeb683f9e45f8066c2