Immutable v4 compatibility

[Velenir]

Closes #46

Also I would like to propose separating immutable dependency into peerDependencies and devDependencies:

"peerDependencies": {
  "immutable": "^3.8.1 || ^4.0.0-rc.1"
},
"devDependencies": {
  "immutable": "^3.8.1 || ^4.0.0-rc.1"
}

That way if a user's project at large uses immutable@^4, redux-immutable won't try to pull in immutable@3.8.1 as a local dependency, but rather import from the project. Avoids bloating up bundle size.

Conditional devDependencies avoids npm warnings when switching between immutable versions in development. 3.8.1 is installed by default.

[gajus]

This looks good. Is is ready to be merged?

[Velenir]

If you agree that immutable dependency should be separated as I proposed, then I'll quickly add a commit with that. Or would you prefer a separate PR?

[gajus]

If you agree that immutable dependency should be separated as I proposed, then I'll quickly add a commit with that.

👍 go for it, this PR is fine.

[Velenir]

Good to go 😄

[gajus]

Thank you

[Velenir]

Thank you for such a useful module.

[jeffchan]

@gajus Thanks for the package! We upgraded to Immutable v4 and noticed that this change, while merged, isn't published to NPM yet. Is it possible to publish it?

[jeffchan]

Nevermind my comment. It is indeed already published as v4.

[andrewmclagan]

Would people consider bumping this to

"peerDependencies": {
  "immutable": "^3.8.1 || ^4.0.0-rc.9"
},
"devDependencies": {
  "immutable": "^3.8.1 || ^4.0.0-rc.9"
}