Use jq instead of jsonlint

As the jsonlint package from NPM causes problems and looks unmaintained,
it'll be replaced with `jq` a well maintained project which allows to
search through JSON files in a `grep`-like style, but knowing the JSON
structure.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

.travis.yml

@@ -32,7 +32,10 @@ jobs:
         - diff -q README.md README.md.orig
       language: generic
     - env: task=json-lint
-      install: npm install jsonlint
+      addons:
+        apt:
+          packages:
+          - jq
       script:
         - npm run jsonlint
       language: generic