Do not install shellcheck for travis.

Author: udhos

Diff for: .travis.yml

@@ -2,13 +2,6 @@ language: bash
 
 sudo: required
 
-addons:
-  apt:
-    sources:
-    - debian-sid    # Grab shellcheck from the Debian repo (o_O)
-    packages:
-    - shellcheck
-
 before_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