Use new dependency resolver for template contract

Created by: HCastano

By default, Cargo's dependency resolver leaks std features from dev-dependencies into no_std builds. This results in confusing errors messages such as the one in https://github.com/paritytech/ink/issues/889.

To avoid issues like this we can use the new(ish) dependency resolver, which doesn't leak features from dev-dependencies into the regular build. You can read more about it here.