In this kata you will create a function that takes a list of non-negative integers and strings and returns a new list with the strings filtered out.
Example:
filter_list([1,2,'a','b']) == [1,2]
filter_list([1,'a','b',0,15]) == [1,0,15]
filter_list([1,2,'aasf','1','123',123]) == [1,2,123]