不了解Rails捆绑器的输出

Question

我正在尝试将项目的rails版本更新为5.2。我更新了Gemfile，如下所示：

gem 'rails', '~> 5.2.1'

运行bundle时，得到以下输出：

Bundler could not find compatible versions for gem "actionmailer":
  In Gemfile:
    devise_invitable was resolved to 1.7.5, which depends on
      actionmailer (>= 4.1.0)

    rails (~> 5.2.1) was resolved to 5.2.2.rc1, which depends on
      actionmailer (= 5.2.2.rc1)

我不明白为什么捆绑程序找不到兼容的版本-5.2.2.rc1既大于4.1.0且等于5.2.2.rc1。我想念什么？