Upgrade go version to >=1.18

[Kaloyan Tanev]

Hi,

Current version of golang is 1.17. Version 1.18 introduces generics which I believe are going to be widely adopted. Unfortunately, upon running swag init I run into errors because of usage of generics. I see the bigger repo swag has already moved to 1.18. Would it be possible to move to >=1.18 here as well?

Cheers!