Update broken link in documentation
Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this [failed invocation](https://github.com/tensorflow/tensorflow/pull/62842/checks?check_run_id=20834329205) of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request. Hi @mihaimaruseac Can you please review this PR ? Thank you!
In ```tensorflow/examples/speech_commands/train.py``` there is a broken link https://aiyprojects.withgoogle.com/open_speech_recording. According to the [internet archive](https://web.archive.org/web/20210402001315/https://aiyprojects.withgoogle.com/open_speech_recording), this has been a broken link since April 2022.

I have replaced the broken link with the Google Blog post about the dataset: https://blog.research.google/2017/08/launching-speech-commands-dataset.html/

This broken link was found with [link-inspector](https://github.com/justindhillon/link-inspector). If you find this useful, please give the repo a :star: