[bugfix][lib][rdbms] Fix issue that column names containing 'update' are replaced

When writing to PostgreSQL using the `ON CONFLICT` statement, columns with names that include the string 'update' were being incorrectly replaced with an empty string. This commit addresses the issue by ensuring that column names are properly handled, even if they contain the substring 'update'.

Author: kingronjan

lib/addax-rdbms/src/main/java/com/wgzhao/addax/rdbms/writer/util/WriterUtil.java

@@ -177,7 +177,7 @@ else if (dataBaseType == DataBaseType.SQLServer) {
 
     private static String doPostgresqlUpdate(String writeMode, List<String> columnHolders)
     {
-        String conflict = writeMode.replace("update", "");
+        String conflict = writeMode.replaceFirst("update", "");
         StringBuilder sb = new StringBuilder();
         sb.append(" ON CONFLICT ");
         sb.append(conflict);