Adding pledge for PLATON

Author: Michael Zhang

_sections/30-projects.md

@@ -73,6 +73,7 @@ These projects pledge to drop Python 2 support in or before 2020.
 - [![](assets/biobuilds.png)BioBuilds](https://www.biobuilds.org/)
 - [![](assets/freud.png)freud](https://github.com/glotzerlab/freud)
 - [![](assets/signac.png)signac](https://signac.io)
+- [![](assets/platon.png)PLATON](https://github.com/ideasrule/platon)
 
 <!-- Adding a new project with a logo? They're roughly sorted by GitHub stars.
 Try to insert yours in order. We use judgment for projects not on GiHhub, and