change dependency on omniauth-oauth2

The dependency on omniauth-oauth2 ~> 1.1.1 prevents the usage of this gem with omniauth-oauth2 version 1.2 (which I need for other omniauth providers such as microsoft and facebook). I tested Clever Instant Login with omniauth-oauth2 1.2.0 and it works so I propose changing the dependency to 1.1.1 and up.