Fix an error for old firefox which doesn't have isSameNode method

[jongsue]

Hello~
I've been using react-sizeme for almost 1 year now.
It's such a great react components for me.

BTW, There is an issue for old firefox browsers.
I found out this bug because my clients are still using old machines :(

I hope you could accept my pull request so I don't modify react-sizeme sources in node_modules folder everytime I build my application

Thank you in advance

[codecov]

Codecov Report

Merging #169 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #169   +/-   ##
=======================================
  Coverage   90.56%   90.56%           
=======================================
  Files           4        4           
  Lines         106      106           
  Branches       25       25           
=======================================
  Hits           96       96           
  Misses          9        9           
  Partials        1        1

Impacted Files	Coverage Δ
src/with-size.js	96.47% <100%> (ø)	⬆️

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[rokoroku]

I also have same issue on Firefox 47

https://developer.mozilla.org/en-US/docs/Web/API/Node/isSameNode#Browser_compatibility

[ctrlplusb]

Apologies for taking a while to get to this. I'll be reviewing this soon. 👍