Rails Tutorial (v.5.1) ハマりポイント 1章 1.3.1項

#この記事はなに
Rails Tutorial (v.5.1) をテキスト通りに進めていた中で、ハマったところの対処メモです。2017.11.16時点。
開発環境はcloud9。
今チュートリアルをやっているくらいなので、Rails初心者です。

#1.3.1 Bundler
##先に結論
bundle update 大事。
##ハマったポイント
Gemfileを指示通りに修正し、bundle install したところ、以下のエラーが発生。

console

user:~/workspace/hello_app (master) $ bundle install
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
You have requested:
  listen = 3.0.8

The bundle currently has listen locked at 3.1.5.
Try running `bundle update listen`

If you are updating multiple gems in your Gemfile at once,
try passing them all to `bundle update`

listen locked at 3.1.5 と記載されているので、それに従ってGemfileを修正。

Gemfile

  gem 'listen', '3.1.5'

そして、再度 bundle install実行。

console

user:~/workspace/hello_app (master) $ bundle install
The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
Fetching gem metadata from https://rubygems.org/.........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Bundler could not find compatible versions for gem "activesupport":
  In snapshot (Gemfile.lock):
    activesupport (= 5.1.4)

  In Gemfile:
    rails (= 5.1.2) was resolved to 5.1.2, which depends on
      activesupport (= 5.1.2)

    coffee-rails (= 4.2.2) was resolved to 4.2.2, which depends on
      railties (>= 4.0.0) was resolved to 5.1.4, which depends on
        activesupport (= 5.1.4)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.

listenに関するエラーはなくなりましたが、activesupportとrailtiesのバージョンが、依存関係でエラーに。
ここもGemfileを直します、、、と思いましたが、依存関係がコンフリクトしてますね。
rails 5.1.2 -> active support 5.1.2
coffee-rails 4.2.2 -> railties 5.1.4 -> active support 5.1.4

どっちのactivesupportを使えばいいんだ。

よく見ると、エラーメッセージに Running bundle update (中略) may resolve the conflict. と書いてあります。

実際に試したところ、うまく解決できました。

console

user:~/workspace/hello_app (master) $ bundle update
(中略)
Bundle updated!
user:~/workspace/hello_app (master) $ bundle install
(中略)
Bundle complete! 16 Gemfile dependencies, 70 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.