Remove jacoco append property
Remove jacoco append property

Jacoco append property is deprecated starting gradle 5.0.
From my understandind the propery is currently ignored.
[Issue Ref](https://github.com/gradle/gradle/issues/5269)

Signed-off-by: Bhargava Varadharajan <6a7e5804810a542d270d24cec4626ae71d02f6ee@gmail.com>

sauliusg/jabref,JabRef/jabref,Siedlerchr/jabref,sauliusg/jabref,Siedlerchr/jabref,sauliusg/jabref,Siedlerchr/jabref,Siedlerchr/jabref,JabRef/jabref,JabRef/jabref,JabRef/jabref,sauliusg/jabref