Fix postgresql integer columns

Version: 2.0.2, Database: PostgreSQL

```javascript
db.define('house', {
  toiletCount: { type: 'number', rational: false }
}).sync();
```

executes:

```sql
CREATE TABLE "house"(
 "id"               SERIAL PRIMARY KEY,
 "toiletCount"  NUMERIC(0)
);
```

which results in:
`ERROR: NUMERIC precision 0 must be between 1 and 1000`

`INTEGER` is a much better choice; From the PostgreSQL docs:

> ...arithmetic on numeric values is very slow compared to the integer types...