Fix Travis build

Author: JElchison

.travis.yml

@@ -11,7 +11,7 @@ install:
  - curl https://ftp-master.debian.org/keys/archive-key-7.0.asc | sudo apt-key add -
  - echo "deb http://ftp.us.debian.org/debian unstable main contrib non-free" | sudo tee -a /etc/apt/sources.list
  - sudo apt-get -qq update
- - sudo apt-get install -y shellcheck
+ - sudo apt-get install -y --allow-unauthenticated shellcheck
  - pip install --user bashate
 
 script: