Fix: support ESLint 4.4.0 (fixes #134)

[mysticatea]

Fixes #134.

This PR fixes the problem that eslint-plugin-vue does not work on ESLint 4.4.0 because it has changed a private API that vue-eslint-parser depends on.

Diff:

• vuejs/vue-eslint-parser@40f48be

The root cause is that vue-eslint-parser depends on a private API in order to traverse <template> separately from the main traversing, but I cannot solve the problem for now.