composerで`knplabs/knp-snappy`を入れる際に`knplabs/knp-snappy suggests installing h4cc/wkhtmltoimage` と言われる

h4cc/wkhtmltopdf-*をインストールするように言われる。

参考URL

現象

  - Installing phpunit/phpunit (3.7.38): Downloading (connecting...)Downloading (100%)         
knplabs/knp-snappy suggests installing h4cc/wkhtmltoimage-amd64 (Provides wkhtmltoimage-amd64 binary for Linux-compatible machines, use version `~0.12` as dependency)
knplabs/knp-snappy suggests installing h4cc/wkhtmltoimage-i386 (Provides wkhtmltoimage-i386 binary for Linux-compatible machines, use version `~0.12` as dependency)
knplabs/knp-snappy suggests installing h4cc/wkhtmltopdf-amd64 (Provides wkhtmltopdf-amd64 binary for Linux-compatible machines, use version `~0.12` as dependency)
knplabs/knp-snappy suggests installing h4cc/wkhtmltopdf-i386 (Provides wkhtmltopdf-i386 binary for Linux-compatible machines, use version `~0.12` as dependency)
knplabs/knp-snappy suggests installing wemersonjanuario/wkhtmltopdf-windows (Provides wkhtmltopdf executable for Windows, use version `~0.12` as dependency)

解決策

composer require h4cc/wkhtmltoimage-amd64
composer require h4cc/wkhtmltoimage-i386
composer require h4cc/wkhtmltopdf-amd64
composer require h4cc/wkhtmltopdf-i386