Support for v3.1 Specs

[AlaNDGT]

Hi,

Are there plan to support version 3.1?

Currently i get the following error:

Unexpected exception. Reason: Cannot read old OpenAPI spec
java.lang.RuntimeException: Cannot read old OpenAPI spec
	at org.openapitools.openapidiff.core.OpenApiCompare.notNull(OpenApiCompare.java:107)
	at org.openapitools.openapidiff.core.OpenApiCompare.fromSpecifications(OpenApiCompare.java:102)
	at org.openapitools.openapidiff.core.OpenApiCompare.fromLocations(OpenApiCompare.java:91)
	at org.openapitools.openapidiff.cli.Main.main(Main.java:174)