fix(overmind): improve merging of hot reloaded state

Author: christianalfoni

packages/node_modules/overmind/src/utils.ts

@@ -59,8 +59,9 @@ export function mergeState(originState, oldState, nextState) {
   function merge(origin, old, next) {
     if (isPlainObject(old) && isPlainObject(next)) {
       const newBranch = {}
+      const keys = Object.keys(old).concat(Object.keys(next))
 
-      for (let key in next) {
+      for (let key of keys) {
         newBranch[key] = merge(origin[key], old[key], next[key])
       }