Update test_likes_function.py

kyu_6/who_likes_it/test_likes_function.py:33 in public class `LikesTestCase`:
        D400: First line should end with a period (not 'n')

        The [first line of a] docstring is a phrase ending in a period.

kyu_6/who_likes_it/test_likes_function.py

@@ -31,7 +31,7 @@
 # pylint: enable=R0801
 class LikesTestCase(unittest.TestCase):
     """
-    Testing likes function
+    Testing likes function.
 
     The function should take in input array, containing the names
     of people who like an item. It must return the display text.