Add bindings for ssrExchange. Upgrade to urql 1.1.3.

[parkerziegler]

This PR adds bindings for the ssrExchange to reason-urql and upgrades our urql dependency to 1.1.3 🎉 This will form the basis of our 1.1.0 release.

While binding this exchange didn't prove to be too difficult, getting a working example with NextJS was non-trivial. For the time being, I decided to skip it. A few things make this really hard:

• The need for a server-side prepass step. I was actually able to successfully bind this: https://github.com/FormidableLabs/bs-react-ssr-prepass. However, the below considerations pushed this over the edge of feasibility currently.
• The need for a higher order component to run the prepass step. Implementing HoCs in Reason is a fairly well known issue and I've never really been able to do it. This is the HoC we'd need to re-implement: https://github.com/FormidableLabs/urql/blob/master/examples/3-ssr-with-nextjs/src/with-urql-client.js Conversely, binding HoCs is possible, and I have an RFC open to create a next-urql package that we'd be able to bind to 🎉 This should make things much easier in the near future, but also make our own support for the ssrExchange a bit moot.
• General problems with having this example in source i.e. challenges with ES6 vs. CommonJs compilation and BuckleScript's weirdness around ES Modules and default imports / exports.

I don't want this feature to hold up development on other parts of reason-urql, so for now I've exposed the bindings and curious souls can venture forth with them if they want to!

@kitten I'd love any thoughts you might have on the above or feelings around how to make SSR easier here. Tagging @Schmavery and @gugahoa as well for visibility.