Update JDBCDemo.java

71和76行测试示例的数据库和表名没有动态拼接，测试用在前面改数据库名和表名，会导致运行报错

tests/examples/JDBC/JDBCDemo/src/main/java/com/taosdata/example/JDBCDemo.java

@@ -68,12 +68,12 @@ public class JDBCDemo {
     }
 
     private void insert() {
-        final String sql = "insert into test.weather (ts, temperature, humidity) values(now, 20.5, 34)";
+        final String sql = "insert into  " + dbName + "." + tbName + " (ts, temperature, humidity) values(now, 20.5, 34)";
         exuete(sql);
     }
 
     private void select() {
-        final String sql = "select * from test.weather";
+        final String sql = "select * from "+ dbName + "." + tbName;
         executeQuery(sql);
     }