Hi @sermakarevich, @jeremy and everyone!

I have a error when counting accuracy:

so when i run

```
log_preds,y = learn.TTA()
probs = np.exp(log_preds)
accuracy(log_preds,y), metrics.log_loss(y, probs)
```

## I get:

```
AttributeError Traceback (most recent call last)
<ipython-input-25-ceca03c60965> in <module>()
1 log_preds,y = learn.TTA()
2 probs = np.exp(log_preds)
----> 3 accuracy(log_preds,y), metrics.log_loss(y, probs)
~/fastai/courses/dl1/fastai/metrics.py in accuracy(preds, targs)
4 def accuracy(preds, targs):
5 preds = np.argmax(preds, axis=1)
----> 6 return (preds==targs).mean()
7
8 def accuracy_thresh(thresh):
`AttributeError: 'bool' object has no attribute 'mean'`
```

it is happens when indicator is 3/4 or 4/4

Do you have some idea how to fix it?