Issue building with JDK 16

When using JDK 16 to build this project it fails with the following error:
```
[ERROR] /jfrunit/src/test/java/dev/morling/jfrunit/StackTraceDisabledSampleEvent.java:[26,8] cannot access jdk.internal.event.Event
  class file for jdk.internal.event.Event not found
[INFO] 1 error
```
I'll try to get more information about it