sql parser improved support db2 truncate syntax. for issue #1324

src/main/java/com/alibaba/druid/sql/dialect/db2/parser/DB2Lexer.java

@@ -38,6 +38,8 @@ public class DB2Lexer extends Lexer {
         map.put("OPTIMIZE", Token.OPTIMIZE);
         map.put("OF", Token.OF);
         map.put("CONCAT", Token.CONCAT);
+        map.put("CONTINUE", Token.CONTINUE);
+        map.put("IDENTITY", Token.IDENTITY);
         
         DEFAULT_DB2_KEYWORDS = new Keywords(map);
     }