Pin flatbuffers version (#1511)

Signed-off-by: Tom Wildenhain <[email protected]>

Author: TomWildenhain-Microsoft

setup.py

@@ -81,7 +81,7 @@ def run(self):
     author='[email protected]',
     author_email='[email protected]',
     url='https://github.com/onnx/tensorflow-onnx',
-    install_requires=['numpy>=1.14.1', 'onnx>=1.4.1', 'requests', 'six', 'flatbuffers'],
+    install_requires=['numpy>=1.14.1', 'onnx>=1.4.1', 'requests', 'six', 'flatbuffers~=1.12'],
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Intended Audience :: Developers',