simply: update to API v2

[ldez]

How to test this PR?

1. You need Go
2. Check out the PR:

   git clone https://github.com/ldez/lego.git
   cd lego
   git checkout feat/dns/simply/api-v2

3. Compile lego:
   • if you have make: make build
   • if you don't make make: go build -o dist/lego ./cmd/lego
4. Run the following command with your information (email, domain, credentials):

   SIMPLY_ACCOUNT_NAME=xxx \
   SIMPLY_API_KEY=xxx \
   ./dist/lego -m [email protected] --dns simply -d '*.example.com' -d example.com -s https://acme-staging-v02.api.letsencrypt.org/directory run

   The wildcard domain is important
5. Before each run of the command, you should clean your local environment:

   rm -rf .lego

Fixes #2630