Your example fails with or without the whitespace. These work though:

Request

  printf 'GET / HTTP/1.1\r\nHost: example.herokuapp.com\r\n\r\n' |  nc example.herokuapp.com 80

Response

  HTTP/1.1 200 OK
  Connection: keep-alive
  Server: SimpleHTTP/0.6 Python/2.7.6

Request

  printf 'GET /  HTTP/1.1\r\nHost: example.herokuapp.com\r\n\r\n' |  nc example.herokuapp.com 80

Response

  HTTP/1.1 505 HTTP Version Not Supported
  Connection: close
  Server: Cowboy