Replace lodash with lodash.<fn> deps

[jakubzitny]

Hey there, we're using react-dnd-html5-backend from NPM and we're quite surprised by the size of the library. The whole react-dnd is taking 4.7M and almost all of that is only lodash. From lodash you're using only memoize, union, without and defaults functions. These are available separately from NPM taking only 148K.

I've already reported similar issue in react-dnd and also #39 might be related to this.

Would you be interested in a PR?

[billyjanitsch]

See react-dnd/react-dnd#517 (comment).

[jakubzitny]

Closing based on the conversation at react-dnd/react-dnd#517.