Adding TensorFlow. (#179)

* Adding TensorFlow.

:tada: TensorFlow will not be supporting Python 2.x as of [January 1, 2020](https://groups.google.com/a/tensorflow.org/forum/m/#!msg/discuss/o5J4rLApPoM/RXoxWuZVAgAJ) -- and, at the time of the this post, had [over 120,000 stars](https://github.com/tensorflow/tensorflow) on GitHub. Happy to move up or down the list, as desired! And thanks so much for creating this site. 😄

* add tf png

Author: dynamicwebpaige

_sections/30-projects.md

@@ -10,6 +10,7 @@ style: center
 
 These projects pledge to drop Python 2 support in or before 2020.
 
+- [![](assets/tensorflow.png)TensorFlow](https://www.tensorflow.org/)
 - [![](assets/pandas.png)pandas](https://pandas.pydata.org/)
 - [![](assets/scikit-learn.png)scikit-learn](https://scikit-learn.org/)
 - [![](assets/tornado.png)Tornado](http://www.tornadoweb.org/)