- Use newer shell pre-commit hooks.

- Use shellcheck from cabal (not the older version in Ubuntu's package
repo which doesn't support --external-sources).

.pre-commit-config.yaml

@@ -4,7 +4,7 @@
     -   id: check-added-large-files
     -   id: check-merge-conflict
 -   repo: https://www.shore.co.il/git/shell-pre-commit/
-    sha: v0.4.0
+    sha: v0.5.4
     hooks:
     -   id: shell-lint
         files: bundle_certs

.travis.yml

@@ -8,23 +8,29 @@ cache:
   - pip
   - directories:
       - $HOME/.pre-commit
+      - $HOME/.cabal
+      - $HOME/.ghc
 
 addons:
   apt:
-    sources:
-      - sourceline: 'deb http://archive.ubuntu.com/ubuntu trusty-backports main universe multiverse'
     packages:
       - mawk
       - openssl
       - curl
       - build-essential
-      - shellcheck
+      - cabal-install
+      - ghc
+
+env:
+    PATH: $PATH:$HOME/.cabal/bin
 
 install:
-  - pip install pre_commit
+  - cabal update && cabal install shellcheck
+  - pip install pre_commit | cat
 
 script:
   - pre-commit run --all-files
 
 notifications:
+  on_failure: never
   email: false