chore(docs): rename @private to @internal

The latter is understood by TypeScript's --stripInternal option, so this lets us
rely more on the tooling provided by typescript team.

modules/angular2/src/core/application_tokens.ts

@@ -2,7 +2,7 @@ import {OpaqueToken, Binding} from 'angular2/src/core/di';
 import {CONST_EXPR, Math, StringWrapper} from 'angular2/src/core/facade/lang';
 
 /**
- *  @private
+ *  @internal
  */
 export const APP_COMPONENT_REF_PROMISE = CONST_EXPR(new OpaqueToken('Promise<ComponentRef>'));