Update to newest Hyperopt

[hirzel]

Hyperopt 0.2.6 was released on November 15: https://pypi.org/project/hyperopt/0.2.6/

Unfortunately, it breaks many Lale tests: https://github.com/IBM/lale/actions/runs/1467468837

For example, the failures include some very basic tests such as:

• test.test_core_transformers.TestFeaturePreprocessing.test_MinMaxScaler
• test.test_core_transformers.TestFeaturePreprocessing.test_PCA
• test.test_core_transformers.TestConcatFeatures.test_concat_with_hyperopt

So for now, we limit the Hyperopt version to <=0.2.5: 24db058

We should try to update to the latest (in fact, if we are lucky, Hyperopt 0.2.7 fixes the problem).

[hirzel]

Update: PR #880 shows that Hyperopt 0.2.7 doesn't just magically fix the problem, so this will require more debugging.