message: Fix lookup ops initialization code snippet in docs.
diff: @@ -1230,8 +1230,8 @@ def index_table_from_file(vocabulary_file=None,
  `[vocabulary size, vocabulary size + num_oov_buckets - 1]`.
  The underlying table must be initialized by calling
  - `session.run(tf.compat.v1.tables_initializer)` or `session.run(table.init)`
  - once.
  + `session.run(tf.compat.v1.tables_initializer())` or
  + `session.run(table.init())` once.
  To specify multi-column vocabulary files, use key_column_index and
  value_column_index and delimiter.
  @@ -1346,8 +1346,8 @@ def index_table_from_tensor(vocabulary_list,
  `[vocabulary list size, vocabulary list size + num_oov_buckets - 1]`.
  The underlying table must be initialized by calling
  - `session.run(tf.compat.v1.tables_initializer)` or `session.run(table.init)`
  - once.
  + `session.run(tf.compat.v1.tables_initializer())` or
  + `session.run(table.init())` once.
  Elements in `vocabulary_list` cannot have duplicates, otherwise when executing
  the table initializer op, it will throw a `FailedPreconditionError`.
  @@ -1444,8 +1444,8 @@ def index_to_string_table_from_file(vocabulary_file,
  (an out-of-vocabulary entry) is assigned the `default_value`
  The underlying table must be initialized by calling
  - `session.run(tf.compat.v1.tables_initializer)` or `session.run(table.init)`
  - once.
  + `session.run(tf.compat.v1.tables_initializer())` or
  + `session.run(table.init())` once.
  To specify multi-column vocabulary files, use key_column_index and
  value_column_index and delimiter.
  @@ -1531,8 +1531,8 @@ def index_to_string_table_from_tensor(vocabulary_list,
  (an out-of-vocabulary entry) is assigned the `default_value`
  The underlying table must be initialized by calling
  - `session.run(tf.compat.v1.tables_initializer)` or `session.run(table.init)`
  - once.
  + `session.run(tf.compat.v1.tables_initializer())` or
  + `session.run(table.init())` once.
  Elements in `vocabulary_list` cannot have duplicates, otherwise when executing
  the table initializer op, it will throw a `FailedPreconditionError`.
  