An error occurred while installing mysql2 (0.5.2), and Bundler cannot continue. Make sure that `gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/'` succeeds before bundling.

git clone して来てbundle
しようとしても、

Fetching mysql2 0.5.2
Installing mysql2 0.5.2 with native extensions

や

An error occurred while installing mysql2 (0.5.2), and Bundler cannot continue.
Make sure that `gem install mysql2 -v '0.5.2' --source 'https://rubygems.org/'` succeeds before bundling.

でつまずいて進まない、、、

ボクの場合の解決方法

rubyのバージョンを-v 2.5.3に変更してGemfile.lockを削除

$ rbenv local 2.5.3
$ sudo rm -rf Gemfile.lock

解決コマンド

$ brew install openssl
$ bundle config --local build.mysql2 "--with-ldflags=-L/usr/local/opt/openssl/lib --with-cppflags=-I/usr/local/opt/openssl/include"

$ bundle install

参考サイト