fix from dubbo:master, 2.5.7 : GenericJSONConverter主要是用在日志部分输出，所以当我们输出locale对象时就发生stack溢出。
```
java.lang.StackOverflowError
	at com.alibaba.dubbo.common.json.JSONWriter.valueString(JSONWriter.java:189)
	at com.alibaba.dubbo.common.json.GenericJSONConverter$7.encode(GenericJSONConverter.java:100)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:338)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:347)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:395)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:347)
	at com.alibaba.dubbo.common.json.GenericJSONConverter.writeValue(GenericJSONConverter.java:395)
```
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
@Deprecated
public class GenericJSONConverter implements JSONConverter {
    private static final String DATE_FORMAT = "yyyy-MM-dd HH:mm:ss";
    private static final Map<Class<?>, Encoder> GlobalEncoderMap = new HashMap<Class<?>, Encoder>();
    private static final Map<Class<?>, Decoder> GlobalDecoderMap = new HashMap<Class<?>, Decoder>();
    static {
        
        Encoder e = new Encoder() {
            @Override
            public void encode(Object obj, JSONWriter jb) throws IOException {
                jb.valueBoolean((Boolean) obj);
            }
        };
        GlobalEncoderMap.put(boolean.class, e);
        GlobalEncoderMap.put(Boolean.class, e);
        e = new Encoder() {
            @Override
            public void encode(Object obj, JSONWriter jb) throws IOException {
                jb.valueInt(((Number) obj).intValue());
            }
        };
        GlobalEncoderMap.put(int.class, e);
        GlobalEncoderMap.put(Integer.class, e);
        GlobalEncoderMap.put(short.class, e);
        GlobalEncoderMap.put(Short.class, e);
        GlobalEncoderMap.put(byte.class, e);
        GlobalEncoderMap.put(Byte.class, e);