Fix: pgsql compatibility

htdocs/install/mysql/migration/3.0.0-3.1.0.sql

@@ -484,4 +484,7 @@ ALTER TABLE llx_don ADD   phone           varchar(24) after email;
 ALTER TABLE llx_user ADD civilite varchar(6) after entity;
 
 ALTER TABLE llx_element_element MODIFY sourcetype varchar(32) NOT NULL;
-ALTER TABLE llx_element_element MODIFY targettype varchar(32) NOT NULL;
\ No newline at end of file
+ALTER TABLE llx_element_element MODIFY targettype varchar(32) NOT NULL;
+
+ALTER TABLE llx_societe_prices MODIFY tms timestamp NULL;
+-- ALTER TABLE llx_societe_prices ALTER COLUMN tms DROP NOT NULL;