Catch pypandoc ModuleNotFoundError

[robin-snt]

Python >= 3.6 doesn't receive ImportError, but instead
ModuleNotFoundError.

I haven't performed exhaustive testing, apart from confirming that the following pattern works on Python 2.7:

try:
    import foobar
except ImportError:
    print 'OK'
except ModuleNotFoundError:
    print 'Never reached on Python 2.7'

I also didn't want to "dry" up the duplicated code since it's short and contains a function definition on the top level scope.

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[pullrequest]

👍 seems good to me provided you confirmed it is actually working locally.

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[martinmr]

Reviewed 1 of 1 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved

[martinmr]

Thanks for the fix.