Write a function called "filter_dict" that takes two parameters, a dictionary
and a number.  The function should removes any entry in the dictionary
that has a value less than or equal to the number.

For example:
>>> my_dict = {'banana': 2, 'apple': 10, 'kiwi': 1}
>>> my_dict
{'kiwi': 1, 'banana': 2, 'apple': 10}
>>> filter_dict(my_dict, 2)
>>> my_dict
{'apple': 10}

We've seen the "del" keyword that deletes a keyword from the dictionary.  One thing
you may notice in writing this function is that if you iterate over a dictionary as follow:

for key in my_dict:
  ...

and then delete an entry, you will get an error.  However, there are other ways of iterating
over things in a dictionary...