Specify environments for non-Solidus global JS variables

We can specify ESLint environments to pre-define global JS variables not
defined by Solidus; this way we can whitelist several vars found within
the project's codebase without the need to specify them one by one

See https://eslint.org/docs/user-guide/configuring#specifying-environments
for details

.eslintrc.json

@@ -1,5 +1,9 @@
 {
  "extends": "airbnb-base",
+ "env": {
+ "browser": true,
+ "jquery": true
+ },
  "rules": {
  "camelcase": 0,
  "comma-dangle": 0,
@@ -29,11 +33,9 @@
  "vars-on-top": 0
  },
  "globals": {
- "$": "readonly",
  "accounting": "readonly",
  "addVariantFromStockLocation": "writable",
  "adjustShipmentItems": "writable",
- "document": "readonly",
  "error": "writable",
  "flatpickr": "readonly",
  "Handlebars": "readonly",
@@ -42,7 +44,6 @@
  "shipments": "writable",
  "Sortable": "readonly",
  "Spree": "readonly",
- "Turbolinks": "readonly",
- "window": "readonly"
+ "Turbolinks": "readonly"
  }
 }