fix: build umd react-is process.env using replace plugin

[jmfrancois]

Following #103 I propose here to follow the proposal of @TrySound
so you can choose:

replace plugin
2.7K hoist-non-react-statics.cjs.js
 15K hoist-non-react-statics.js
3.4K hoist-non-react-statics.min.js

without react-is from #103
2.7K  hoist-non-react-statics.cjs.js
3.3K hoist-non-react-statics.js
1.2K hoist-non-react-statics.min.js

[coveralls]

Coverage remained the same at 88.05% when pulling d96328f on jmfrancois:jmfrancois/fix/umd-replace into f3de655 on mridgway:master.

[alippai]

While it's useful for development, I don't think a library should leak proptypes and react-is at all, it should be removed upon publishing.