DOC: find kernelspec
xref https://github.com/pydata/pandas/pull/13487

Problem was the notebook was written with a python3 kernel, but the doc build is python2. 
There are potentially problems here if you have non-default kernel names in your environment...

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13491?src=pr) is **84.33%**

> Merging [#13491](https://codecov.io/gh/pydata/pandas/pull/13491?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

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  Misses         8000       8000          
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> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [b01e07e...cb967e1](https://codecov.io/gh/pydata/pandas/compare/b01e07e3395f7cee5a9922af979ea41aa40ff892...cb967e14b67fdc16932f7f6de1a2755f50032648)
 Isn't there a way to say "use the same kernel as the one that is calling me"? 
Because this will only work for "python2"/"python3" kernel names, which is OK for travis, but eg locally I build the docs mainly with my 'dev' environment for which I have a kernel named 'dev'
 I couldn't find anything like that immediately. Will look tonight.
 No matter, if I build the docs from that environment, the kernel will be named python2/3 anyhow, it's only when I select in the notebook the kernel itself (starting the notebook from another environment), that the name of this kernel will be different.
 There is a difference between kernel name and display name in the `kernelspec`
 Let's give it another try! :-) 
 https://travis-ci.org/pydata/pandas/jobs/138920776 is the build.
 Hmm, still not working: "Failed to convert source/html-styling.ipynb" in the logs
 Just saw that 😞, I'll look into it more later.
