BUG: fix klucher nan output for numpy

[mikofski]

• fixes klucher results different between pandas and numpy #508
• use F = np.where(np.isnan(F), 0, F) to only replace nan with zero
• previously if numpy array with nan, then entire array was zeroed so output differed from pandas series input

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The following items must be addressed before the code can be merged. Please don't hesitate to ask for help if you're unsure of how to accomplish any of the items below:

• Closes issue #xxxx
• I am familiar with the contributing guidelines.
• Fully tested. Added and/or modified tests to ensure correct behavior for all reasonable inputs. Tests (usually) must pass on the TravisCI and Appveyor testing services.
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate docs/sphinx/source/whatsnew file for all changes.
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Brief description of the problem and proposed solution (if not already fully described in the issue linked to above):

[mikofski]

FYI: @jdnewmil

[wholmgren]

Thanks @mikofski! I think we only need to see a whatsnew entry before merging. The test errors are unrelated.

[mikofski]

@wholmgren this patch is passing all tests, the failure is due to "703165TYA.CSV" not having any content so readtmy3() fails

[mikofski]

@wholmgren I added what's new, all good now?

[wholmgren]

thanks mark!