querying `launches` returns errors on "final" repo.

It seems the tutorial is out of date, as even the final returns errors, so I know it isn't with my implementation after going through the tutorial.

The playground returns the following after running the `GetLaunches` query from the tutorial:

```
{
"error": {
"errors": [
{
"message": "Cannot query field \"id\" on type \"LaunchConnection\".",
"locations": [
{
"line": 3,
"column": 5
}
],
"extensions": {
"code": "GRAPHQL_VALIDATION_FAILED",
"exception": {
"stacktrace": [
"GraphQLError: Cannot query field \"id\" on type \"LaunchConnection\".",
" at Object.Field (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/validation/rules/FieldsOnCorrectType.js:64:31)",
" at Object.enter (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:333:29)",
" at Object.enter (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:384:25)",
" at visit (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:251:26)",
" at Object.validate (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/validation/validate.js:63:22)",
" at validate (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:172:32)",
" at Object. (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:113:38)",
" at Generator.next ()",
" at fulfilled (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:4:58)",
" at process._tickCallback (internal/process/next_tick.js:68:7)"
]
}
}
},
{
"message": "Cannot query field \"mission\" on type \"LaunchConnection\".",
"locations": [
{
"line": 4,
"column": 5
}
],
"extensions": {
"code": "GRAPHQL_VALIDATION_FAILED",
"exception": {
"stacktrace": [
"GraphQLError: Cannot query field \"mission\" on type \"LaunchConnection\".",
" at Object.Field (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/validation/rules/FieldsOnCorrectType.js:64:31)",
" at Object.enter (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:333:29)",
" at Object.enter (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:384:25)",
" at visit (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/language/visitor.js:251:26)",
" at Object.validate (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/graphql/validation/validate.js:63:22)",
" at validate (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:172:32)",
" at Object. (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:113:38)",
" at Generator.next ()",
" at fulfilled (/home/petty/Github/apollo-graphql/fullstack-tutorial/final/server/node_modules/apollo-server-core/dist/requestPipeline.js:4:58)",
" at process._tickCallback (internal/process/next_tick.js:68:7)"
]
}
}
}
]
}
}
```

final/server のチュートリアル実装から始め、playground の GetLaunches クエリで使用されているスキーマを調べます。クエリが要求しているフィールドを LaunchConnection 型およびチュートリアルの本文と比較します。ドキュメントに記載されたクエリが最終的なスキーマと一致し、GraphQL の検証エラーなしで実行できれば完了です。

索引モデルが issue の本文から書いたものです。