Use shallowCompare from right place

[zpao]

We never shipped it in React.addons. It should be used from require('react-addons-shallow-compare').

(previously filed as facebook/react#4315).

cc @pocketjoso @jardakotesovec

[cpojer]

The sad thing about this is that I'll have to add a require/import statement which is hard :)

[jketcham]

Can there be something mentioning this in the README perhaps? I just stumbled upon this problem when using react-codemod to update from 13.3 to 14.2, and reading it beforehand would've helped the troubleshooting when upgrading.

[cpojer]

I don't think anyone is going to get to this and it's now been so long that few people actually need this particular codemod, so I'm going to go ahead and close this.