message: Add missing library to install instructions
diff: - sudo yum groupinstall -y 'Development Tools'
  - sudo yum install -y update
  - sudo yum install -y git
  -- sudo yum install -y openssl-devel libgmp3-dev cmake
  +- sudo yum install -y openssl-devel libgmp3-dev cmake zlib1g-dev
  #### Mac Osx
  - /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
  