Installation Steps:

Open Terminal using Spotlight search by pressing  <command+space>.
Type terminal and hit  Enter key.

• Now, run
  ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)” < /dev/null 2> /dev/null
• Install cfn-lint using brew
  brew install cfn-lint

cfn-lint is ready to use now!