Take x-nullable into consideration for oas2 valid examples

[igas]

Describe the bug

oas2-valid-response-schema-example does not consider x-nullable

To Reproduce

1. clone https://github.com/igas/examples-examples
2. spectral lint oas2.yaml
3. See error 63:24 error oas2-valid-response-schema-example nickname property type should be string

Expected behavior
Because nickname has x-nullable I expect it not to raise error

Additional context
I believe it's related to #1284 as it started failing with 5.5.0 upgrade attempt

[igas]

Thanks @P0lip!

[corroded]

@P0lip Curious why this was reverted in master? 621c025

[P0lip]

@corroded Hey. I had to revert it since patch-package didn't work too well with npm installations of Spectral.
Binaries worked just fine. I'll revisit it soon - I'm hoping to get it out in one of the next releases.