Update README.md

Author: thomasrockhu

README.md

@@ -7,6 +7,7 @@ Add to your `.travis.yml` file.
 language: java
 
 # Cobertura is not supported in JDK11 so you must downgrade the JDK that Travis uses if you want to use Cobertura with Travis.
+# See https://github.com/cobertura/cobertura/issues/381
 jdk:
   - openjdk8