Fix IllegalAccessError for Scala 2.12

[kanderson250]

Follow up for #2272

We discovered the source of the scala IllegalAccessError for apps with Scala 2.12 and JRE 11+: the major version of classfiles getting updated to the runtime version (despite having been compiled into Java 8).

Update the agent to mitigate this behavior.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-386254