Bump to 2.2.0

Author: bdukes

elm.json

@@ -3,7 +3,7 @@
     "name": "EngageSoftware/elm-dnn-http",
     "summary": "Helpers for working with DNN Web API",
     "license": "Apache-2.0",
-    "version": "2.1.0",
+    "version": "2.2.0",
     "elm-version": "0.19.0 <= v < 0.20.0",
     "exposed-modules": [
         "Engage.Http"