Add ESLint Hound configuration

Before, Hound had its own default ESLint configuration. We are moving
these configurations into specific organisations. Added a
thoughtbot-specific Hound configuration for ES6 files.

https://trello.com/c/HY2hoTdq

Author: Rob Whittaker

.hound.yml

@@ -1,6 +1,9 @@
 coffeescript:
   enabled: true
   config_file: style/coffeescript/coffeelint.json
+eslint:
+  enabled: true
+  config_file: style/eslint/.eslintrc
 haml:
   enabled: true
   config_file: style/haml/haml.yml

style/eslint/.eslintrc

@@ -0,0 +1,8 @@
+{
+  "rules": {},
+  "env": {
+    "es6": true,
+    "browser": true
+  },
+  "extends": "eslint:recommended"
+}