Don't use object spread (for compatibility reasons)

src/index.js

@@ -171,14 +171,14 @@ class ToJsonSchema {
 
   commmonPostProcessDefault(type, schema, value) { // eslint-disable-line no-unused-vars
     if (this.options.required) {
-      return {...schema, required: true}
+      return merge({}, schema, {required: true})
     }
     return schema
   }
 
   objectPostProcessDefault(schema, obj) {
     if (this.options.objects.additionalProperties === false && Object.getOwnPropertyNames(obj).length > 0) {
-      return {...schema, additionalProperties: false}
+      return merge({}, schema, {additionalProperties: false})
     }
     return schema
   }

test/schema/objects.js

@@ -2,6 +2,7 @@
 
 const should = require('chai').should()
 const omit = require('lodash.omit')
+const merge = require('lodash.merge')
 
 const testSchemaWithAndWithoutMerge = require('../helpers/testSchema').tesSchemaWithAndWithoutArrayMerge
 const testSchemaNormal = require('../helpers/testSchema').testSchemaWithoutArrayMerge
@@ -211,7 +212,7 @@ describe('Objects', () => {
     it('should return proper schema when postProcessFnc is used', () => {
       const options = {
         postProcessFnc: (type, schema, value, defaultFunc) =>
-          (type === 'integer') ? {...schema, required: true} : defaultFunc(type, schema, value),
+          (type === 'integer') ? merge({}, schema, {required: true}) : defaultFunc(type, schema, value),
       }
 
       const instance = {
@@ -341,7 +342,8 @@ describe('Objects', () => {
     it('Custom objects.postProcessFnc makes properties required on parent type level', () => {
       const options = {
         objects: {
-          postProcessFnc: (schema, obj, defaultFnc) => ({...defaultFnc(schema, obj), required: Object.getOwnPropertyNames(obj)}),
+          postProcessFnc: (schema, obj, defaultFnc) =>
+            (merge({}, defaultFnc(schema, obj), {required: Object.getOwnPropertyNames(obj)})),
         },
       }
       testSchemaNormal({}, {type: 'object', required: []}, options)