Update angular-translate.d.ts

Update defintions to match Angular Translate v2.3.0
I think string to any, not only ITranslateProvider.

https://github.com/angular-translate/angular-translate/blob/d548b0351f75e6a36991319305ea2d122f2c2f37/src/translate.js#L18
I think it seems to string | ITranslateProvider. TypeScript can't provide union types...