Fix eslint error

* upgrade eslint

* fix eslint error

package.json

@@ -52,7 +52,7 @@
     "babel-runtime": "^5.8.0",
     "casperjs": "^1.1.0-beta5",
     "codecov.io": "^0.1.2",
-    "eslint": "^2.1.0",
+    "eslint": "^2.9.0",
     "eslint-config-vue": "^1.0.0",
     "istanbul-instrumenter-loader": "^0.1.3",
     "jasmine-core": "^2.4.1",

test/unit/specs/util/dom_spec.js

@@ -31,7 +31,7 @@ describe('Util - DOM', function () {
       done()
     }
     document.body.appendChild(f)
-    f.src = "about:blank"
+    f.src = 'about:blank'
   })
 
   it('getAttr', function () {