DNS lexicon 3.1.0 changes

[knoxell]

From #10 :

As written in certbot pull request in dns-lexicon v3.1.0 the variable type parameter was renamed to rtype, which makes it incompatible with older certbot versions.

Solutions:

1. require dns-lexicon<3.1.0 only for NPM, maybe in NPM config?
2. implement create_record and delete_record and pass arguments without names as suggested here
3. (2.2) try and catch around a call with rtype and type and possibly use super(NamecheapClient,self).*_record(...)

One of these should still be done.