Remove unneccassary cast to URLClassLoader, which breaks on JDK 11

Author: tgodzik

sbt-bridge/src/xsbt/CompilerClassLoader.java

@@ -110,7 +110,7 @@ private static ClassLoader computeFixedLoader(ClassLoader bridgeLoader) {
       Field parentBField = dualLoaderClass.getDeclaredField("parentB");
       parentBField.setAccessible(true);
       URLClassLoader scalaLoader = (URLClassLoader) parentAField.get(dualLoader);
-      URLClassLoader sbtLoader = (URLClassLoader) parentBField.get(dualLoader);
+      ClassLoader sbtLoader = (ClassLoader) parentBField.get(dualLoader);
 
       URL[] bridgeURLs = urlBridgeLoader.getURLs();
       return new URLClassLoader(bridgeURLs,