fix(overmind-react): fix flush listener in SSR

Author: christianalfoni

packages/node_modules/overmind/src/index.ts

@@ -94,9 +94,11 @@ export function createOvermindSSR<Config extends IConfiguration>(
     } as SSRMode
   ) as any
 
-  ssr.state = ssr.proxyStateTree.getMutationTree().state
+  const mutationTree = ssr.proxyStateTree.getMutationTree()
+
+  ssr.state = mutationTree.state
   ssr.hydrate = () => {
-    return (ssr as any).proxyStateTree.mutationTree.flush().mutations
+    return mutationTree.flush().mutations
   }
   return ssr
 }