chore(server): update pubspec to include http_server

… since it is needed by the server source (had thought that it was
there before, but apparently not; maybe I was working from a stale
cache).
fix(recipe_book): apply chap 6 updates to chap 7 code
Merge pull request #100 from chalin/patch-0312-server-pubspec

chore(server): update pubspec to include http_server
Merge pull request #101 from chalin/patch-0312-ch7-updates-from-ch6

fix(recipe_book): apply chap 6 updates to chap 7 code