Housekeeping eslint (#516)

* dev build threw some errors with eslint for me, so I added what was missing. Please review.

* added babel-eslint package to devDependencies
* added eslint config to support ES6
* added another .eslintrc file in the test folder to make eslint aware of jasmine globals.

* small config correction of eslint

.eslintrc

@@ -1,4 +1,8 @@
 {
   "root": true,
+  "parser": "babel-eslint",
+  "parserOptions": {
+    "sourceType": "module"
+  },
   "extends": "vue"
 }

package.json

@@ -37,6 +37,7 @@
   "homepage": "https://github.com/vuejs/vuex#readme",
   "devDependencies": {
     "babel-core": "^6.2.1",
+    "babel-eslint": "^7.1.1",
     "babel-loader": "^6.2.0",
     "babel-plugin-transform-runtime": "^6.1.18",
     "babel-polyfill": "^6.2.0",

test/unit/.eslintrc

@@ -0,0 +1,5 @@
+{
+  "env": {
+    "jasmine": true
+  }
+}