Update tf_records.ipynb
Update tf_records.ipynb

"a the" -> "a" (or "the"?)

Also, I realised that the online docs don't precisely match this source - especially the end of the [Writing a TFRecord file](https://www.tensorflow.org/tutorials/load_data/tf_records#writing_a_tfrecord_file) section, where it says:
`# the return type is <a href="../../api_docs/python/tf#string"><code>tf.string</code></a>.`
instead of # the return type is `tf.string`.\n",
tensorflow/docs,tensorflow/docs,tensorflow/docs