improved oracle sql parser.

src/main/java/com/alibaba/druid/sql/parser/Token.java

@@ -95,7 +95,8 @@ public enum Token {
     CASE("CASE"), 
     WHEN("WHEN"), 
     THEN("THEN"), 
-    ELSE("ELSE"), 
+    ELSE("ELSE"),
+    ELSIF("ELSIF"),
     END("END"), 
     EXISTS("EXISTS"), 
     IN("IN"),