Fix tensorflow warnings

[panchbhai1969]

Command:

python build_vocab.py data/monument_300/data_300.en > data/monument_300/vocab.en

Output:

WARNING:tensorflow:From build_vocab.py:43: __init__ (from tensorflow.contrib.learn.python.learn.preprocessing.text) is deprecated and will be removed in a future version.
Instructions for updating:
Please use tensorflow/transform or tf.data.
WARNING:tensorflow:From /home/petrichor/.local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/preprocessing/text.py:154: __init__ (from tensorflow.contrib.learn.python.learn.preprocessing.categorical_vocabulary) is deprecated and will be removed in a future version.
Instructions for updating:
Please use tensorflow/transform or tf.data.
WARNING:tensorflow:From /home/petrichor/.local/lib/python2.7/site-packages/tensorflow/contrib/learn/python/learn/preprocessing/text.py:170: tokenizer (from tensorflow.contrib.learn.python.learn.preprocessing.text) is deprecated and will be removed in a future version.
Instructions for updating:
Please use tensorflow/transform or tf.data.

Follow the updating instructions to handle these warnings.