fetchBoilerplateMapping() {
    const { pkgInfo } = this;
    const mapping = pkgInfo.boilerplates;
    for (const key of Object.keys(mapping)) {
      const item = mapping[key];
      item.name = item.name || key;
      item.from = pkgInfo;
    }
    return mapping;
  }
fetch boilerplate mapping from `package.json`
@return {Object} boilerplate config mapping,
`{
  simple: {
    "name": "admin",
    "package": "beidou-template-simple",
    "description": "Simple beidou isomorphic app boilerplate"
  }
}`