upgrade getkin/kin-openapi to v0.80.0 to fix panic when server is missing a path (#474)

Co-authored-by: Marcin Romaszewicz <47459980+deepmap-marcinr@users.noreply.github.com>

Author: mikezuff

oapi_validate_test.go

@@ -36,7 +36,7 @@ info:
   version: 1.0.0
   title: TestServer
 servers:
-  - url: http://deepmap.ai/
+  - url: http://deepmap.ai
 paths:
   /resource:
     get: