acknowledge Flask-Caching in THIRDPARTY.md

THIRDPARTY.md

@@ -85,3 +85,18 @@ URL: https://bitty-js.com/
 License: CC0 1.0  
 Author: alan w smith https://www.alanwsmith.com/  
 Repo: https://github.com/alanwsmith/bitty  
+
+## Flask-Caching
+
+URL: https://flask-caching.readthedocs.io/  
+Copyright:
+
+```
+Copyright (c) 2010 by Thadeus Burgess.
+Copyright (c) 2016 by Peter Justin.
+
+Some rights reserved.
+```
+
+License: BSD-3-Clause ([see more](https://github.com/pallets-eco/flask-caching/blob/e59bc040cd47cd2b43e501d636d43d442c50b3ff/LICENSE))  
+Repo: https://github.com/pallets-eco/flask-caching