Fix Cython compiled check in ipython

[dmontagu]

Addresses the issue raised in #548 related to running non-compiled in IPython

[dmontagu]

@samuelcolvin Not sure why the build is failing. It says

2:58:53 PM: Running Sphinx v2.0.1
2:58:54 PM: Configuration error:
2:58:54 PM: There is a programmable error in your configuration file:
2:58:54 PM: Traceback (most recent call last):
2:58:54 PM:   File "/opt/buildhome/python3.6/lib/python3.6/site-packages/sphinx/config.py", line 361, in eval_config_file
2:58:54 PM:     execfile_(filename, namespace)
2:58:54 PM:   File "/opt/buildhome/python3.6/lib/python3.6/site-packages/sphinx/util/pycompat.py", line 86, in execfile_
2:58:54 PM:     exec(code, _globals)
2:58:54 PM:   File "/opt/build/repo/docs/conf.py", line 85, in <module>
2:58:54 PM:     from pydantic.version import VERSION
2:58:54 PM:   File "pydantic/__init__.py", line 2, in init pydantic.__init__
2:58:54 PM:   File "pydantic/dataclasses.py", line 8, in init pydantic.dataclasses
2:58:54 PM:   File "pydantic/main.py", line 68, in init pydantic.main
2:58:54 PM: NameError: name 'cython' is not defined

in the build logs (https://app.netlify.com/sites/pydantic-docs/deploys/5cf5977b10a4b80009431880), but I don't understand how the change I made could have introduced this error.

Also, the tests pass for me locally whether or not I have cython installed in the testing environment.

[samuelcolvin]

No idea why this fails, but it does. Both on travis and netlify.

wrap this in an AttributeError try/except and add pragma: no cover wherever required.

Please add an entry to history too.

[codecov]

Codecov Report

Merging #573 into master will not change coverage.
The diff coverage is n/a.

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