Optimize the comment about class loader

[tianshuang]

In HotSpot JVM, javaseClassLoader is actually Extension ClassLoader, The comment of javaseClassLoader mentioned:

    /**
     * The bootstrap class loader used to load the JavaSE classes. In some
     * implementations this class loader is always <code>null</code> and in
     * those cases {@link ClassLoader#getParent()} will be called recursively on
     * the system class loader and the last non-null result used.
     */
    private ClassLoader javaseClassLoader;

So I think it is more appropriate to use bootstrap classLoader in the comments.

[markt-asf]

Thanks for the PR. I agree bootstrap is a better description of the class loader being used.