message: Fix the comments of tf.contrib.lookup.MutableHashTable insert operation
diff: @@ -298,7 +298,7 @@ class MutableHashTable(LookupInterface):
  table = tf.contrib.lookup.MutableHashTable(key_dtype=tf.string,
  value_dtype=tf.int64,
  default_value=-1)
  - table.insert(keys, values)
  + sess.run(table.insert(keys, values))
  out = table.lookup(query_keys)
  print(out.eval())
  ```
  @@ -494,7 +494,7 @@ class MutableDenseHashTable(LookupInterface):
  value_dtype=tf.int64,
  default_value=-1,
  empty_key=0)
  - table.insert(keys, values)
  + sess.run(table.insert(keys, values))
  out = table.lookup(query_keys)
  print(out.eval())
  ```
  