[eslint] Add browser to the environment

Test Plan:
  - Things like window and document shouldn't show as issues when
    used.

Change-Id: Iec96aec6d823d74536fb92e6e44b430bca7a5f02
Reviewed-on: https://gerrit.instructure.com/94145
Tested-by: Jenkins
Reviewed-by: Dan Minkevitch <dan@instructure.com>
Product-Review: Clay Diffrient <cdiffrient@instructure.com>
QA-Review: Clay Diffrient <cdiffrient@instructure.com>

Author: claydiffrient

.eslintrc.json

@@ -1,9 +1,13 @@
 {
   "env": {
     "es6": true,
-    "amd": true
+    "amd": true,
+    "browser": true
   },
   "extends": "airbnb",
+  "globals": {
+    "ENV": true
+  },
   "parserOptions": {
     "ecmaVersion": 7,
     "ecmaFeatures": {

spec/javascripts/.eslintrc.json

@@ -1,6 +1,5 @@
 {
     "env": {
-        "amd": true,
         "qunit": true
     },
     "globals": {