Fix wrong mysql date format cause fatal error when MySQL in strict mode

When mysql runs with 
```
@@sql_mode=NO_ENGINE_SUBSTITUTION
```
Save/update products via Models_Mapper_ProductMapper::getInstance()->save($product) cause 

```
SQLSTATE[22007]: Invalid datetime format: 1292 Incorrect datetime value: '2014-08-08T12:57:58+03:00' for column 'updated_at' 
```

Fixed with use of proper format. :shipit: