SSR and responsive mode

I already open [this issue on the nextjs repo](https://github.com/zeit/next.js/issues/4398) but it seems to be a problem with react-slick.

**Describe the bug**
When I use next.js with react-slick and responsive options, there is a bug during the rehydration phase, the src attribute of the images are mixed between the slides.

The error message is `Warning: Prop src did not match. Server: "http://via.placeholder.com/350x150?text=7" Client: "http://via.placeholder.com/350x150?text=8"`

**To Reproduce**
I made an example from examples folder : https://github.com/padupuy/next.js/tree/feature/with-react-slick

The code is right here : https://github.com/padupuy/next.js/blob/feature/with-react-slick/examples/with-react-slick/pages/index.js

**Expected behavior**
The image sources must *not* be mixed

**Screenshots**


**System information**
- OS: macOS High Sierra 10.13.4
- Browser (if applies) : at least chrome and safari
- Version of Next.js: at least 5.1 and 6.0.2