feat(proxy-state-tree): also handle delete mutation revert value

Author: christianalfoni

packages/node_modules/proxy-state-tree/src/Proxyfier.ts

@@ -336,6 +336,7 @@ export class Proxifier {
             path: nestedPath,
             args: [],
             hasChangedValue: true,
+            revertValue: target[prop],
           },
           objectChangePath
         )

packages/node_modules/proxy-state-tree/src/index.test.ts

@@ -242,6 +242,7 @@ describe('OBJECTS', () => {
           path: 'foo',
           args: [],
           hasChangedValue: true,
+          revertValue: 'bar',
         },
       ])
       expect(mutationTree.state.foo).toBe(undefined)