Fixed typo in tearDown fn

Tutorials/T5/src/test_statistics.py

@@ -13,7 +13,7 @@ class StatisticsTests(unittest.TestCase):
         self.circles = [c1,c2,c3,c4,c5]
 
     def tearDown(self):
-        self.circle = None
+        self.circles = None
 
     def testAverageOfCircles(self):
         self.assertAlmostEqual(average(self.circles), 2000000003.45,  None, None, 0.1)
@@ -25,4 +25,4 @@ class StatisticsTests(unittest.TestCase):
         self.assertAlmostEqual(stdDev(self.circles), 3999999998.275, None, None, 0.1)
 
 if __name__ == '__main__':
-    unittest.main()
\ No newline at end of file
+    unittest.main()