gemの特定のバージョンが配信停止になった時の対処法(the author of mimemagic 0.3.5 has removed it)

エラー文

Fetching gem metadata from https://rubygems.org/............
Your bundle is locked to mimemagic (0.3.5), but that version could not be found
in any of the sources listed in your Gemfile. If you haven't changed sources,
that means the author of mimemagic (0.3.5) has removed it. You'll need to update
your bundle to a version other than mimemagic (0.3.5) that hasn't been removed
in order to install.

大事な部分切り取る

that means the author of mimemagic (0.3.5) has removed it. You'll need to update

解決方法

bundle update mimemagic