fix SSR v-show render.

[defcc]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:

SSR v-show directive should be merged from parent to child component.

It could be reproduced via this github repo.

And the demo code is bellow:

var Vue = require('vue/dist/vue.common.js')
var createRenderer = require('vue-server-renderer').createRenderer
var renderToString = createRenderer().renderToString

const vm = new Vue({
  template: `
    <foo v-show="false"></foo>
  `,
  components: {
    foo: {
      render: h => h('bar'),
      components: {
        bar: {
          render: h => h('div', 'inner')
        }
      }
    }

  }
})

renderToString(vm, (err, res) => {
  console.log(res)
})

The result is <div server-rendered="true">inner</div>, it should be <div server-rendered="true" style="display:none;">inner</div>