language: bash
sudo: required
dist: trusty
before_install:
  - echo "deb http://archive.ubuntu.com/ubuntu/ trusty-backports universe" | sudo tee -a /etc/apt/sources.list
  - sudo apt-get update -qq
  - sudo apt-get install shellcheck -y
script:
  - shellcheck $(find . -maxdepth 1 -type f -executable)

language: bash
sudo: required
dist: trusty
addons:
  apt:
    sources:
      - sourceline: "deb http://archive.ubuntu.com/ubuntu/ trusty-backports universe"
    packages:
      - shellcheck
script:
  - shellcheck $(find . -maxdepth 1 -type f -executable)

Install `shellcheck` using `apt` addon
Install `shellcheck` using `apt` addon