Fixed encoding problem, added simple people spec and checked when the response is invalid

I was trying the Tmdb::People.latest method and an exception was raised because of this:
```
etag = response.headers['etag'].gsub /"/, ''
```

Then, I fixed it and I realized that the service from TMDB was actually broken: http://api.themoviedb.org/3/people/latest?api_key=8a221fc31fcdf12a8af827465574ffc9

Once I was in the project I have also fixed a problem with the encoding of the file movie_spec.rb and added the file people_spec.rb, a very simple version though, but I think it could be useful.

I hope it's ok, the specs are passing and if you think it's better to have 3 pull requests, one for every change, I can do it too.

Thank you for this great gem.