Fix: more robust parser setting (fixes #30)

Author: mysticatea

Diff for: lib/config/base.js

@@ -1,7 +1,7 @@
 module.exports = {
   root: true,
 
-  parser: 'vue-eslint-parser',
+  parser: require.resolve('vue-eslint-parser'),
 
   parserOptions: {
     ecmaVersion: 6,