use tf.shape instead of .shape for dynamic axes

Signed-off-by: masakistan <sfujimoto@gmail.com>

Author: masakistan

onnx_tf/handlers/backend/instance_normalization.py

@@ -31,7 +31,7 @@ def _common(cls, node, **kwargs):
     beta = tensor_dict[node.inputs[2]]
 
     inputs = tensor_dict[node.inputs[0]]
-    inputs_shape = inputs.shape
+    inputs_shape = tf.shape(inputs)
     inputs_rank = inputs.shape.ndims
 
     moments_axes = list(range(inputs_rank))[2:]