I created a very basic test project to try out Flow. I have a USB to serial cable connected and have it plugged into a board The project is very much like your example Terminal application
The Main File
THe exception occurs when running IO(Serial) ! Open
This is the exception: java.lang.UnsupportedClassVersionError: com/github/jodersky/flow/internal/NativeSerial : Unsupported major.minor version 51.0