Put upper bound back to 50

This puts the upper bound for the randomly determined sample size
back to 50. The immediately preceding commits verified that the
bug can be fixed by a change in the lower bound, but we don't
always want to use a lower bound of 2!

It may be best to choose the sample size non-randomly, perhaps
testing multiple sample sizes per run using parametrization or
subtests. But that is more extensive than the small change needed
for bazingagin#45, and thus beyond the scope here.

tests/test_knn_classifier.py

@@ -116,7 +116,7 @@ def test_predict(self) -> None:
         assert labels.shape == (1,)
         assert similar_samples.shape == (top_k, 1)
 
-        test_set_size = random.randint(2, 2)  # FIXME: Put upper bound back to 50.
+        test_set_size = random.randint(2, 50)
         test_set = [self.sample_input for _ in range(test_set_size)]
         top_k = 2
         (distance, labels, similar_samples) = self.model.predict(test_set, top_k)