catch and log errors thrown when calling React.findDOMNode

[chimericdream]

This is mainly a band-aid so that exceptions thrown when checking a DOM node don't crash a React app. It logs the offending component and error to the console.

Given how the library hooks itself into the component lifecycle, I didn't want to try and remove the use of findDOMNode entirely, even though it is deprecated in the newer releases of React/ReactDOM. At a glance, that looks like it will be rather non-trivial to change how react-axe listens for component updates.

Closes issue: #74

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[CLAassistant]

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[stephenmathieson]

LGTM, but let's use console.error() for logging the error.

[stephenmathieson]

Thanks!