private static ClassLoader getClassLoader() {
		ClassLoader ret = Thread.currentThread().getContextClassLoader();
		return ret != null ? ret : PathKit.class.getClassLoader();
	}
private static ClassLoader getClassLoader ( ) { ClassLoader ret = Thread . currentThread ( ) . getContextClassLoader ( ) ; return ret != null ? ret : PathKit . class . getClassLoader ( ) ; }
优先使用 current thread 所使用的 ClassLoader 去获取路径
否则在某些情况下会获取到 tomcat 的 ClassLoader，那么路径值将是
TOMCAT_HOME/lib

issue: https://gitee.com/jfinal/jfinal/issues/ID428#note_699360