Remove non-essential dev dependency

The `standard` module has a ton of dependencies and enforcing
a coding style for this rarely-modified repo doesn't seem worth
the extra dependency (and resulting `npm audit` failures).

Developers can continue to run the linter locally as appropriate.

.travis.yml

@@ -3,8 +3,6 @@ language: node_js
 node_js:
 - node
 script:
-- npm run lint
 - npm run check-security
 dist: trusty
-sudo: false
 os: linux