Fails on is_prime(5). Returns None when it should return True

It looks like the other corrected examples in the Q&A to me.

```
def is_prime(x):
if x <= 1:
return False
elif x == 2:
return True
elif x > 3:
for n in range(2, x-1):
if x % n == 0:
return False
else:
return True
```