Find the second-to-last element of a list.
Example:
```python
penultimate([1,2,3,4])            # => 3
penultimate(["Python is dynamic"]) # => 'i'
(courtesy of [haskell.org](http://www.haskell.org/haskellwiki/99_questions/1_to_10))
```
def penultimate(a):
  # implement here
  try:
      return a[-2]
  except:
      return None
def penultimate(a):
  # implement here
  try:
      return a[-2]
  except:
      return None