j4rs v0.25 not compatible with class file v52

[jonpas]

j4rs v0.24 works perfectly, but v0.25.0 and higher when used with Java 8 (JDK 1.8) results in:

DEBUG: Invoking static method run of class com.apollo.persistence.Handler using 1 arguments
Exception in thread "Thread-0" java.lang.UnsupportedClassVersionError: org/astonbitecode/j4rs/api/instantiation/NativeInstantiationImpl has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:473)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351)

thread 'main' (410045) panicked at src/lib.rs:65:10:
called `Result::unwrap()` on an `Err` value: JavaError("An Exception was thrown by Java while creating global ref... Please check the logs or the console.")

Looks like some dependency is causing use of class version 55, while Java 8 supports only class version 52. This is related to #54.

I understand if there is no wish to support file version 52 anymore, but in case there is, I decided to open this issue.