Adds support for the video poster attribute (#1123)

Author: RomansBermans

template/build/vue-loader.conf.js

@@ -14,7 +14,7 @@ module.exports = {
  cssSourceMap: sourceMapEnabled,
  cacheBusting: config.dev.cacheBusting,
  transformToRequire: {
- video: 'src',
+ video: ['src', 'poster'],
  source: 'src',
  img: 'src',
  image: 'xlink:href'