incompatible api diff result when one of property in model becomes not required

if in new api version some property is not required anymore, new api is recognized as not compatible

old api schema definition:
```
"SomeDto": {
        "required": [
          "prop1",
          "prop2",
          "prop3"
        ], ...
```
new api schema definition:

```
"SomeDto": {
        "required": [
          "prop1"
        ], ...
```