fix flaky test serializeReadOnlyStringProperty

Author: xinying7

modules/swagger-core/src/test/java/io/swagger/v3/core/serialization/properties/PropertySerializationTest.java

@@ -295,8 +295,11 @@ public void deserializeArrayStringProperty() throws IOException {
     @Test(description = "it should serialize a string property with readOnly set")
     public void serializeReadOnlyStringProperty() throws IOException {
         final Schema p = new StringSchema().readOnly(true);
-        final String json = "{\"type\":\"string\",\"readOnly\":true}";
-        assertEquals(m.writeValueAsString(p), json);
+        final String json1 = "{\"type\":\"string\",\"readOnly\":true}";
+        String json2 = m.writeValueAsString(p);
+        JSONObject jsonObj1 = new JSONObject(json1);
+        JSONObject jsonObj2 = new JSONObject(json2);
+        JSONAssert.assertEquals(jsonObj1, jsonObj2, true);
     }
 
     @Test(description = "it should serialize a string property with readOnly unset")