3.1 exclusiveMinimum and exclusiveMaximum are unsupported by external dependency

[charjr]

Currently, neither cebe/php-openapi nor devizzent/cebe-php-openapi are capable of supporting numeric values for exclusiveMinimum nor exclusiveMaximum.

I've made a PR to try and fix this DEVizzent/cebe-php-openapi#23

Alternatives:

• Remove dependency and parse openapi independently
• Do not use external validation from these libraries, perhaps requiring a try-catch for type errors.

Obviously the former is cleaner, but the latter is quicker.

[charjr]

The external dependency is now capable of supporting numeric exclusiveMinimum and exclusiveMaximum.

It still has a default of false though. So we cannot fully validate whether the user provided it correctly. So we will have to assume, for 3.1, that if exclusiveMinimum or exclusiveMaximum are set to false that they have been omitted.