Avoid a breaking change by keeping expires_on and deprecate it instead

lib/dnsimple/struct/domain.rb

@@ -36,7 +36,20 @@ class Domain < Base
 
       # @return [String] When the domain was last updated in DNSimple.
       attr_accessor :updated_at
-    end
 
+      # @deprecated Please use #expires_at instead.
+      # @return [String] The date the domain will expire.
+      def expires_on
+        warn "[DEPRECATION] Domain#expires_on is deprecated. Please use `expires_at` instead."
+        Date.parse(expires_at).to_s if expires_at
+      end
+
+      # @deprecated Please use #expires_at= instead.
+      # @param expiration_date The date the domain will expire
+      def expires_on=(expiration_date)
+        warn "[DEPRECATION] Domain#expires_on= is deprecated. Please use `expires_at=` instead."
+        expires_at = DateTime.parse(expiration_date) if expiration_date
+      end
+    end
   end
 end

spec/dnsimple/client/domains_spec.rb

@@ -153,6 +153,7 @@
       expect(result.auto_renew).to be(false)
       expect(result.private_whois).to be(false)
       expect(result.expires_at).to eq("2021-06-05T02:15:00Z")
+      expect(result.expires_on).to eq("2021-06-05")
       expect(result.created_at).to eq("2020-06-04T19:15:14Z")
       expect(result.updated_at).to eq("2020-06-04T19:15:21Z")
     end