Create a function that returns the data type of a given variable. These are the seven data types this challenge will be testing for:
data_type([1, 2, 3, 4]) ➞ "list"
data_type({'key': "value"}) ➞ "dictionary"
data_type("This is an example string.") ➞ "string"
data_type(datetime.date(2018,1,1)) ➞ "date"
Return the name of the data type as a lowercase string.