Update 02 broken links of lstm-text-generation example in README.md

[gaikwadrahul8]

I have updated 02 broken links on this page, one is for model saving API hyperlink on this line "This example also illustrates how to save a trained model in the browser's IndexedDB using TensorFlow.js's model saving API".

Second is for LSTM text generation example from Keras on this line "This example is inspired by the LSTM text generation example from Keras: https://github.com/keras-team/keras/blob/master/examples/lstm_text_generation.py" at the moment I have updated broken link to this link https://github.com/keras-team/keras-io/blob/master/examples/generative/lstm_character_level_text_generation.py because I believe there is no previous LSTM text generation example from Keras available now, I checked on keras website under Text generation example section so I recommend that we change the broken link to https://github.com/keras-team/keras-io/blob/master/examples/generative/lstm_character_level_text_generation.py If you agree, please do the needful. Thank you!