Provide ability to lint JSON files (#167)

* Upgrade js-yaml sub-dependency from 3.12.1 to 3.13.0 for DoS fix

* Update eslint to 5.16

Only new rule is prefer-named-capture-group, which is a ECMAScript 2018
feature, so we can ignore it.

* Provide ability to lint JSON files (Fixes #166)

Users will have to adjust the src match from *.js to also cover JSON
files, but there's no need to set the `extensions` options value as
well.

* test: Run eslint for json files too

* build: Update js-yaml locked dependency for audit

common.json

@@ -2,6 +2,7 @@
   "extends": "eslint:recommended",
   "env": {},
   "globals": {},
+  "plugins": [ "json" ],
   "rules": {
     "array-bracket-spacing": [ "error", "always" ],
     "block-spacing": "error",

package.json

@@ -4,7 +4,7 @@
   "description": "ESLint config following Wikimedia code conventions.",
   "main": "common.json",
   "scripts": {
-    "test": "eslint --report-unused-disable-directives . && node test/test.js",
+    "test": "eslint --report-unused-disable-directives . --ext .js,.json && node test/test.js",
     "build-invalid": "node test/test.js dump"
   },
   "repository": {
@@ -44,7 +44,8 @@
   ],
   "license": "MIT",
   "dependencies": {
-    "eslint": "^5.14.0",
+    "eslint": "^5.16.0",
+    "eslint-plugin-json": "^1.4.0",
     "eslint-plugin-no-jquery": "^2.0.0",
     "eslint-plugin-qunit": "^4.0.0"
   },