Update __init__.py to properly expose KerasTransformer via 'from sparkdl import KerasTransformer' (#96)

Author: smurching

python/sparkdl/__init__.py

@@ -17,6 +17,7 @@
 from .image.imageIO import imageSchema, imageType, readImages
 from .transformers.keras_image import KerasImageFileTransformer
 from .transformers.named_image import DeepImagePredictor, DeepImageFeaturizer
+from .transformers.keras_tensor import KerasTransformer
 from .transformers.tf_image import TFImageTransformer
 from .transformers.tf_tensor import TFTransformer
 from .transformers.utils import imageInputPlaceholder