Standard Charset object used; other warnings fixed

src/org/jetbrains/java/decompiler/main/decompiler/ConsoleDecompiler.java

@@ -172,7 +172,7 @@ public class ConsoleDecompiler implements IBytecodeProvider, IResultSaver {
   @Override
   public void saveClassFile(String path, String qualifiedName, String entryName, String content, int[] mapping) {
     File file = new File(getAbsolutePath(path), entryName);
-    try (Writer out = new OutputStreamWriter(new FileOutputStream(file), "UTF8")) {
+    try (Writer out = new OutputStreamWriter(new FileOutputStream(file), StandardCharsets.UTF_8)) {
       out.write(content);
     }
     catch (IOException ex) {