security/rubygem-omniauth-alicloud: Fix gemspec for rubygem-omniauth-oauth2
1.8.0 update
- Bump PORTREVISION for package change
The code is identical in 1.7.1 and 1.8.0. The only different is omniauth version
(~> 2.0).
Reference: https://github.com/omniauth/omniauth-oauth2/compare/v1.7.3...v1.8.0