pin to the older tf2onnx

Author: wenbingl

.azure-pipelines/linux-CI-nightly.yml

@@ -37,7 +37,7 @@ jobs:
       conda install -c conda-forge cmake
       python -m pip install $(ONNX_PATH)
       python -m pip install tensorflow-cpu==1.15.0
-      python -m pip install tf2onnx
+      python -m pip install tf2onnx==1.5.6
       python -m pip install git+https://github.com/microsoft/[email protected]
       python -m pip install git+https://github.com/onnx/[email protected]
       python -m pip install -r requirements.txt

.azure-pipelines/win32-CI-nightly.yml

@@ -38,7 +38,7 @@ jobs:
       echo Test numpy installation... && python -c "import numpy"
       pip install %COREML_PATH% %ONNX_PATH%
       python -m pip install tensorflow-cpu==1.15.0
-      python -m pip install tf2onnx
+      python -m pip install tf2onnx==1.5.6
       python -m pip install git+https://github.com/microsoft/onnxconverter-common@@r1.7
       python -m pip install git+https://github.com/onnx/keras-onnx@@r1.7
       echo Test onnxconverter-common installation... && python -c "import onnxconverter_common"