Fixed tfe.Variable error (#7674)

After Eager was moved to core Tensorflow, this notebook gives the error:
AttributeError: module 'tensorflow.contrib.eager' has no attribute 'Variable'
I just fixed it.

research/nst_blogpost/4_Neural_Style_Transfer_with_Eager_Execution.ipynb

@@ -169,7 +169,6 @@
       "cell_type": "code",
       "source": [
         "import tensorflow as tf\n",
-        "import tensorflow.contrib.eager as tfe\n",
         "\n",
         "from tensorflow.python.keras.preprocessing import image as kp_image\n",
         "from tensorflow.python.keras import models \n",
@@ -826,7 +825,7 @@
         "  \n",
         "  # Set initial image\n",
         "  init_image = load_and_process_img(content_path)\n",
-        "  init_image = tfe.Variable(init_image, dtype=tf.float32)\n",
+        "  init_image = tf.Variable(init_image, dtype=tf.float32)\n",
         "  # Create our optimizer\n",
         "  opt = tf.train.AdamOptimizer(learning_rate=5, beta1=0.99, epsilon=1e-1)\n",
         "\n",