Build Java code to be compatible with older Java (#5965)
Build Java code to be compatible with older Java (#5965)

## What is the goal of this PR?

Currently, we compile Grakn on CI with Java 11. This could result in unexpected runtime issues when running on older Java, such as `java.lang.NoSuchMethodError: java.nio.ByteBuffer.flip()Ljava/nio/ByteBuffer;` that we experienced.

## What are the changes implemented in this PR?

Pass Java compiler option to produce bytecode compatible with Java 8
graknlabs/grakn,lolski/grakn,graknlabs/grakn,graknlabs/grakn,lolski/grakn,lolski/grakn,lolski/grakn,graknlabs/grakn