fix docs in next page

Author: SaraVieira

core/server-side-rendering.md

@@ -218,15 +218,15 @@ import { createHook } from "overmind-react";
 export const config = {
   state: {},
   actions: {
-  add
-    changePage({ state }, mutations) {
-      rehydrate(state, mutations || []);
-    }
-  }
+    add: {
+      changePage({ state }, mutations) {
+        rehydrate(state, mutations || []);
+      },
+    },
+  },
 };
 
 export const useOvermind = createHook();
-
 ```
 
 And you are all set to get going with `overmind` and `next.js`. You can also take a look at [this example in the next.js examples directory](https://github.com/vercel/next.js/tree/canary/examples/with-overmind) if you need some help.