[Improvement] follow eslint-plugin-vue strongly-recommended code style (#482)

package.json

@@ -66,7 +66,7 @@
     "css-loader": "^0.28.7",
     "dependency-tree": "^5.12.0",
     "eslint": "^4.13.1",
-    "eslint-plugin-vue": "^2.1.0",
+    "eslint-plugin-vue": "^4.0.0-beta.4",
     "extract-text-webpack-plugin": "3.0.2",
     "fast-vue-md-loader": "^1.0.3",
     "friendly-errors-webpack-plugin": "^1.6.1",
@@ -95,7 +95,7 @@
     "style-loader": "^0.19.1",
     "uppercamelcase": "^3.0.0",
     "url-loader": "^0.6.2",
-    "vant-doc": "0.3.19",
+    "vant-doc": "0.3.20",
     "vue": "^2.5.13",
     "vue-loader": "^13.6.1",
     "vue-router": "^3.0.1",