train_time_limit not working?

Hi all,

Since I have a large dataset to predict, I'm using `train_time_limit` as a setting to fit automl as below (as introduced in #65 ). However, it does not seem to work as the `automl.best_config_train_time` is still greater than this number (20).

Many thanks!

```
settings = {
"time_budget": 200,
"metric": 'r2',
"estimator_list": ['lgbm'],
"task": 'regression',
"train_time_limit": 20,
"seed": 7654321,
}
automl.fit(X_train=training, y_train=training_labels, **settings)
```