官网说的是这样的：
但实际上，应该是这样修改：
{
"presets": [
["env", {
"targets": {
"browsers": ["> 1%", "last 2 versions", "not ie <= 8"]
}
}],
"stage-2"
],
"plugins": [
"transform-vue-jsx",
"transform-runtime",
["component", {
"libraryName": "element-ui",
"styleLibraryName": "theme-chalk"
}]
]
}