provide classloader to NativeLibrary.getInstance

When multiple classloaders are active, the current call to NativeLibrary.getInstance may fail to find the shared library resource (JNA will use the thread context classloader, which is unlikely to be the correct one).

It works if the correct classloader is provided, like this:

public static final NativeLibrary JNA_NATIVE_LIB = NativeLibrary.getInstance(HunspellLibrary.JNA_LIBRARY_NAME, HunspellLibrary.class.getClassLoader());