Image classification training error: Unable to find an entry point named 'TF_StringEncodedSize' in shared library 'tensorflow'

Greetings,

running the [Train a deep learning image classification model with ML.NET and TensorFlow](https://docs.microsoft.com/en-us/samples/dotnet/machinelearning-samples/mlnet-image-classification-transfer-learning/) example as-it throws the following exception:

```
I tensorflow/core/platform/profile_utils/cpu_utils.cc:112] CPU Frequency: 2299965000 Hz
Unhandled exception. System.EntryPointNotFoundException: Unable to find an entry point named 'TF_StringEncodedSize' in shared library 'tensorflow'.
at Tensorflow.c_api.TF_StringEncodedSize(UInt64 len)
at Microsoft.ML.Vision.ImageClassificationTrainer.EncodeByteAsString(VBuffer`1 buffer)
at Microsoft.ML.Vision.ImageClassificationTrainer.ImageProcessor.ProcessImage(VBuffer`1& imageBuffer)
at Microsoft.ML.Vision.ImageClassificationTrainer.CacheFeaturizedImagesToDisk(IDataView input, String labelColumnName, String imageColumnName, ImageProcessor imageProcessor, String inputTensorName, String outputTensorName, String cacheFilePath, Dataset dataset, Action`1 metricsCallback, Nullable`1 validationFraction)
at Microsoft.ML.Vision.ImageClassificationTrainer.TrainModelCore(TrainContext trainContext)
at Microsoft.ML.Trainers.TrainerEstimatorBase`2.TrainTransformer(IDataView trainSet, IDataView validationSet, IPredictor initPredictor)
at Microsoft.ML.Trainers.TrainerEstimatorBase`2.Fit(IDataView input)
at Microsoft.ML.Data.EstimatorChain`1.Fit(IDataView input)
at DeepLearning_ImageClassification.Program.Main(String[] args)
```

Is this an issue with the sample, or with the ML.net implementation?