fix default charset issue

apollo-client/src/main/java/com/ctrip/framework/apollo/util/http/HttpUtil.java

@@ -16,6 +16,7 @@ import com.google.common.base.Function;
 import com.google.common.io.BaseEncoding;
 import com.google.common.io.CharStreams;
 import com.google.gson.Gson;
+import java.nio.charset.StandardCharsets;
 
 /**
  * @author Jason Song(song_s@ctrip.com)
@@ -104,7 +105,7 @@ public class HttpUtil {
       statusCode = conn.getResponseCode();
 
       if (statusCode == 200) {
-        isr = new InputStreamReader(conn.getInputStream());
+        isr = new InputStreamReader(conn.getInputStream(), StandardCharsets.UTF_8);
         String content = CharStreams.toString(isr);
         return new HttpResponse<>(statusCode, serializeFunction.apply(content));
       }