Couldn't re-exec init when yarn failed on init

```
root@syzoj-test-vm:~/syzoj-ng-app# commitizen init cz-conventional-changelog --yarn --dev --exact
Attempting to initialize using the npm package cz-conventional-changelog
yarn add v1.19.0
[1/4] Resolving packages...
[2/4] Fetching packages...
error Incorrect integrity when fetching from the cache
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
root@syzoj-test-vm:~/syzoj-ng-app# commitizen init cz-conventional-changelog --yarn --dev --exact
Attempting to initialize using the npm package cz-conventional-changelog
Error: Error: A previous adapter is already configured. Use --force to override
adapterConfig.path: ./node_modules/cz-conventional-changelog
repoPath: /root/syzoj-ng-app
CLI_PATH: /usr/local/share/.config/yarn/global/node_modules/commitizen/
installAdapterCommand: yarn add cz-conventional-changelog --dev --exact
adapterNpmName: cz-conventional-changelog
```

Only removing the new entries from `package.json` can I run the init command again.

まず、`commitizen init cz-conventional-changelog --yarn --dev --exact` コマンドを再現し、`package.json` に作成されるエントリ周辺の初期化フローを調査します。Yarn のインストールに失敗しても古い adapter 設定が残らず、同じ init コマンドを `package.json` を手動で編集せずに再実行できれば、修正は完了です。

索引モデルが issue の本文から書いたものです。