Fixed minor bug in mnist example

Author: MohamedNourArm

tensorflow_model_optimization/python/examples/clustering/keras/mnist/mnist_cnn.py

@@ -22,10 +22,11 @@
 from absl import app as absl_app
 from absl import flags
 
-import tensorflow.compat.v1 as tf
-from tensorflow.python import keras
+import tensorflow as tf
 from tensorflow_model_optimization.python.core.clustering.keras import cluster
+from tensorflow_model_optimization.python.core.clustering.keras import cluster_config
 
+keras = tf.keras
 l = keras.layers
 
 FLAGS = flags.FLAGS
@@ -96,7 +97,7 @@ def train_and_save(models, x_train, y_train, x_test, y_test):
 
     clustering_params = {
       'number_of_clusters': 8,
-      'cluster_centroids_init': 'density-based'
+      'cluster_centroids_init': cluster_config.CentroidInitialization.DENSITY_BASED
     }
 
     # Cluster model