message: default to current origin in app config
diff: @@ -17,7 +17,7 @@ export class AppConfig {
  // if null, use node passed by auth token v1.3 or otherwise core.blockstack.org
  coreNode: string
  - constructor(appDomain: string,
  + constructor(appDomain: string = window.location.origin,
  scopes: Array<string> = DEFAULT_SCOPE.slice(),
  redirectPath: string = '/',
  manifestPath: string = '/manifest.json',
  