fix license badge link

Author: gruns

README.md

@@ -5,7 +5,7 @@
 <p align="center">
   <a href="https://pypi.python.org/pypi/icecream"><img src="https://badge.fury.io/py/icecream.svg"></a>
   <a href="https://github.com/gruns/icecream/actions/workflows/ci.yml"><img src="https://github.com/gruns/icecream/actions/workflows/ci.yml/badge.svg"></a>
-  <a href="http://unlicense.org/"><img src="https://img.shields.io/pypi/l/icecream.svg"></a>
+  <a href="/LICENSE.txt"><img src="https://img.shields.io/pypi/l/icecream.svg"></a>
   <a href="https://pypi.python.org/pypi/icecream"><img src="https://img.shields.io/pypi/pyversions/icecream.svg"></a>
 </p>