Fix m.login.appservice -> m.login.application_service (#3711)

* Fix m.login.appservice -> m.login.application_service

Implementations seem to agree with the proposal, so I'd suggest we fix the typo in the spec. I don't *think* this needs a MSC as the original proposal was fine, and this was just a copy error.

* Create 3711.clarification

* Update 3711.clarification

* Update changelogs/3711.clarification

Co-authored-by: Travis Ralston <travisr@matrix.org>

Co-authored-by: Travis Ralston <travisr@matrix.org>

changelogs/3711.clarification

@@ -0,0 +1 @@
+Fix incorrectly referenced `m.login.appservice` login identifier, instead using `m.login.application_service`.

content/client-server-api/_index.md

@@ -1087,7 +1087,7 @@ To use this login type, clients should submit a `/login` request as follows:
 
 ```json
 {
-  "type": "m.login.appservice",
+  "type": "m.login.application_service",
   "identifier": {
     "type": "m.id.user",
     "user": "<user_id or user localpart>"