Update ONNX docs with the latest supported ONNX version (apache#11936)

docs/api/python/contrib/onnx.md

@@ -13,7 +13,7 @@ With ONNX format support for MXNet, developers can build and train models with a
 ```
 
 ### Installation Instructions
-- To use this module developers need to **install ONNX**, which requires the protobuf compiler to be installed separately. Please follow the [instructions to install ONNX and its dependencies](https://github.com/onnx/onnx#installation). **MXNet currently supports ONNX v1.1.1**. Once installed, you can go through the tutorials on how to use this module.
+- To use this module developers need to **install ONNX**, which requires the protobuf compiler to be installed separately. Please follow the [instructions to install ONNX and its dependencies](https://github.com/onnx/onnx#installation). **MXNet currently supports ONNX v1.2.1**. Once installed, you can go through the tutorials on how to use this module.
 
 
 This document describes all the ONNX-MXNet APIs.
@@ -24,6 +24,7 @@ This document describes all the ONNX-MXNet APIs.
 
     mxnet.contrib.onnx.import_model
     mxnet.contrib.onnx.get_model_metadata
+    mxnet.contrib.onnx.import_to_gluon
     mxnet.contrib.onnx.export_model
 ```
 
@@ -49,10 +50,10 @@ This document describes all the ONNX-MXNet APIs.
 
 ```eval_rst
 
-.. automodule:: mxnet.contrib.onnx
-    :members: import_model
-    :members: get_model_metadata
-    :members: export_model
+.. automodule:: mxnet.contrib.onnx.import_model
+.. automodule:: mxnet.contrib.onnx.get_model_metadata
+.. automodule:: mxnet.contrib.onnx.import_to_gluon
+.. automodule:: mxnet.contrib.onnx.export_model
 
 ```