HMR does not works when work with unplugin-vue-router

[liuwilliamBUPT]

reproduces: vue-layout-demo

I find when use pagesDirs or layoutsDirs options, the hmr will fail.

After I checked the code, I find if one of the options set, canEnableClientLayout will return false.Then simple hmr will not be use.

At this line, a watcher will listen dirs without config.root path prepended. So when hmr start, this will no module match the file name, and the page will not refresh.

I think this line may be changed to

watcher.add(layoutDirs)

And I've tested it, it work for the reproduce.

[markthree]

duplicate of #142，Let's track #141