fix(0.4/2015-07-07--salt_and_hash.xml): don't use ALTER TABLE MODIFY on PostgreSQL.

The failure was:
liquibase.exception.DatabaseException: ERROR: syntax error at or near "MODIFY"
Position: 22 [Failed SQL: ALTER TABLE users MODIFY COLUMN hash VARCHAR(60) NOT NULL]

Addressed to #1034

Author: php-coder

src/main/resources/liquibase/version/0.4/2015-07-07--salt_and_hash.xml

@@ -19,11 +19,17 @@
 			We can't use modifyDataType because it looses not null setting:
 			http://forum.liquibase.org/topic/warning-of-losing-primary-key-autoincrement-for-mysql
 		-->
-		<sql>
+		<sql dbms="mysql,h2">
 			ALTER TABLE users
 			MODIFY COLUMN hash VARCHAR(60) NOT NULL
 		</sql>
 
+		<sql dbms="postgresql">
+			ALTER TABLE users
+			ALTER COLUMN hash
+			TYPE VARCHAR(60)
+		</sql>
+		
 	</changeSet>
 
 	<changeSet id="migrate-test-users-passwords-hashes" author="php-coder" context="test-data">