[Ch4Nb09] Fixed some errors and path issues

1.	Updated tensorflow from '1.14.0' to '2.4.0 '.
2.	Fixed 'tf.gfile.GFile' to 'tf.io.gfile.GFile'.
3.     'from keras.utils.np_utils import to_categorical' is the change.
4.	Added try block for windows and colab users and specified the path for downloading files for windows users.

Author: jatinpapreja