适配jdk1.6

pu/pu/src/private/org/jeecg/common/util/HttpHelper.java

@@ -8,7 +8,6 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
-import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.UUID;