message: Match identity server registration to the IS r0.3.0 spec
  The returned field is `token` for the spec, but we somehow got through with `access_token` on Sydent.
diff: @@ -183,8 +183,10 @@ export default class IdentityAuthClient {
  async registerForToken(check=true) {
  try {
  const hsOpenIdToken = await MatrixClientPeg.get().getOpenIdToken();
  - const { access_token: identityAccessToken } =
  + // XXX: The spec is `token`, but we used `access_token` for a Sydent release.
  + const { access_token, token } =
  await this._matrixClient.registerWithIdentityServer(hsOpenIdToken);
  + let identityAccessToken = token ? token : access_token;
  if (check) await this._checkToken(identityAccessToken);
  return identityAccessToken;
  } catch (e) {
  