Update README.md

Author: tzaeschke

README.md

@@ -31,7 +31,7 @@ In 2019 and 2020 development was kindly supported by [Improbable](https://improb
 <dependency>
     <groupId>ch.ethz.globis.phtree</groupId>
     <artifactId>phtree</artifactId>
-    <version>2.8.0</version>
+    <version>2.8.1</version>
 </dependency>
 ```
 
@@ -46,6 +46,11 @@ You can create GitHub Issues or contact me on [Discord](https://discord.gg/GNYjy
 
 # News
 
+### 2024-06-22
+Release 2.8.1
+- Fixed NPE problem with getStats() on empty tree
+- Fixed warning and refreshed dependencies
+
 ### 2023-07-29
 Release 2.8.0  (2.7.0 was a dud)
 - Use MinMaxHeap for kNN in v13, v16 and v16HD.