V 0.7.5.1 Hot fix for scikit-learn 0.22 update and some other bug fixes

[yzhao062]

All Submissions Basics:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you checked all Issues to tie the PR to a specific one?

All Submissions Cores:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?
• Does your submission pass tests, including CircleCI, Travis CI, and AppVeyor?
• Does your submission have appropriate code coverage? The cutoff threshold is 95% by Coversall.

New Model Submissions:

• Have you created a .py in ~/pyod/models/?
• Have you created a _example.py in ~/examples/?
• Have you created a test_.py in ~/pyod/test/?
• Have you lint your code locally prior to submission?

Error Log:
https://travis-ci.org/yzhao062/pyod/builds/620977046

[coveralls]

Pull Request Test Coverage Report for Build 1233

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 95.202%

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Files with Coverage Reduction	New Missed Lines	%
pyod/models/base.py	1	95.49%

Totals
Change from base Build 1155:	-0.01%
Covered Lines:	11964
Relevant Lines:	12567

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💛 - Coveralls