refactor keywords

sharding-jdbc-core/src/main/java/com/dangdang/ddframe/rdb/sharding/parsing/lexer/dialect/mysql/MySQLKeyword.java

@@ -32,8 +32,6 @@ public enum MySQLKeyword implements Keyword {
     OFFSET, 
     VALUE, 
     BEGIN, 
-    TRUE, 
-    FALSE, 
     FORCE, 
     PARTITION, 
     DISTINCTROW, 

sharding-jdbc-core/src/main/java/com/dangdang/ddframe/rdb/sharding/parsing/lexer/dialect/postgresql/PostgreSQLKeyword.java

@@ -28,8 +28,6 @@ public enum PostgreSQLKeyword implements Keyword {
     
     SHOW,
     ONLY,
-    TRUE,
-    FALSE,
     ARRAY,
     FIRST,
     NEXT,

sharding-jdbc-core/src/main/java/com/dangdang/ddframe/rdb/sharding/parsing/lexer/token/DefaultKeyword.java

@@ -51,6 +51,8 @@ public enum DefaultKeyword implements Keyword {
     BY,
     WITH,
     WITHOUT,
+    TRUE,
+    FALSE,
     TEMPORARY,
     TEMP,
     COMMENT,