Update instance_normalization.py

switch to onnx helper func tf_shape instead of tf.shape

Author: masakistan

onnx_tf/handlers/backend/instance_normalization.py

@@ -3,6 +3,7 @@
 from onnx_tf.handlers.backend_handler import BackendHandler
 from onnx_tf.handlers.handler import onnx_op
 from onnx_tf.handlers.handler import tf_func
+from onnx_tf.common.tf_helper import tf_shape
 
 
 @onnx_op("InstanceNormalization")
@@ -31,7 +32,7 @@ def _common(cls, node, **kwargs):
     beta = tensor_dict[node.inputs[2]]
 
     inputs = tensor_dict[node.inputs[0]]
-    inputs_shape = tf.shape(inputs)
+    inputs_shape = tf_shape(inputs)
     inputs_rank = inputs.shape.ndims
 
     moments_axes = list(range(inputs_rank))[2:]