Java 8 support

[steph4nc]

The CacheLoader and AsyncCacheLoader fail on Java 8 projects. I see in the fork network, someone else ran into the same issue and this is the commit they added: BinaryMan32@badd0c3

However, I also see on Caffeine's releases page, that the new version 3 does not support Java 8 and to rather use version 2 for Java 8 support https://github.com/ben-manes/caffeine/releases/tag/v3.0.0

So potentially we need a version of Scaffeine that runs on the latest V3 and another version that runs on the latest V2 for Java 8.

[blemale]

👋 Hi @steph4nc !
Contributions are welcome so feel free to submit a PR to fix this issue if you want.
I will not do it myself as I'm not using this project at work neither I work with Scala anymore.
BTW the Java baseline for recent caffeine version, ie 3.x, is Java 11.

[seeni-dev]

If it helps anyone, I downgraded scaffeine version to 4.1.0, which depends on 2.x of caffeine and it worked.
I was using basic features of Cache. So it didn't throw any problems. https://search.maven.org/artifact/com.github.blemale/scaffeine_2.12/4.1.0/jar