Fixed final test_axographio.py test for Python 3

In Python 2, round() always returns a float. In Python 3, the original data type is returned. For this test, the rounded value had type numpy.float32, which is not considered equivalent to a float in Python 3 (64-bit machines only, presumably). Fixed by converting the value to a float before rounding.

test_axographio.py

@@ -57,7 +57,7 @@ def test_graphfile(self):
             self.assertEqual(len(d), 2048)
         self.assertEqual(round(sum(file.data[1]),13), -2.1483816e-6)
         self.assertEqual(round(sum(file.data[2]),13), -1.4318602e-6)
-        self.assertEqual(round(file.data[0][2047],6), 1.024)
+        self.assertEqual(round(float(file.data[0][2047]),6), 1.024)
 
 
     def test_axograph_x_file(self):