added note about Java 10 support

groovy/content.md

@@ -25,4 +25,4 @@ docker volume create --name grapes-cache
 docker run --rm -it -v grapes-cache:/home/groovy/.groovy/grapes %%IMAGE%%
 ```
 
-**Note: Java 9 support is experimental**
+**Note: Java 9 and Java 10 support is experimental**