build.test can never be red

Assertion errors need to be passed to the mocha `done` callback, otherwise the test will appear to be green.

[These lines](https://github.com/sequelize/sequelize-auto/blob/master/test/build.test.js#L38-L42) should be changed to 

```
    auto.build().then(tableData => {
      callback(tableData);
      done();
    }).catch((e) => {
      done(e);
    })
```