docs: add col length of example

docs/zh/14-reference/03-connector/java.mdx

@@ -368,7 +368,7 @@ public class ParameterBindingDemo {
 
     private static final String host = "127.0.0.1";
     private static final Random random = new Random(System.currentTimeMillis());
-    private static final int BINARY_COLUMN_SIZE = 20;
+    private static final int BINARY_COLUMN_SIZE = 30;
     private static final String[] schemaList = {
             "create table stable1(ts timestamp, f1 tinyint, f2 smallint, f3 int, f4 bigint) tags(t1 tinyint, t2 smallint, t3 int, t4 bigint)",
             "create table stable2(ts timestamp, f1 float, f2 double) tags(t1 float, t2 double)",