vite preview responses with initial html although html has been rebuilt

[Sociosarbis]

Describe the bug

vite preview responses with initial html (latest one is expected) although html has been rebuilt.

dev option for sirv should set to true.

I will make a PR for this.

The reason for

Reproduction

1. yarn vite build (with build.watch)
2. yarn vite serve
3. change some codes in your project to make rebuild automatically

System Info

Output of npx envinfo --system --npmPackages vite,@vitejs/plugin-vue --binaries --browsers:

  System:
    OS: Windows 10 10.0.18363
    CPU: (8) x64 Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz
    Memory: 613.61 MB / 7.90 GB
  Binaries:
    Node: 12.14.0 - D:\nodejs\node.EXE
    Yarn: 1.12.3 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
    npm: 6.13.4 - D:\nodejs\npm.CMD
  Browsers:
    Chrome: 90.0.4430.212
    Edge: Spartan (44.18362.449.0)
    Internet Explorer: 11.0.18362.1
  npmPackages:
    @vitejs/plugin-vue: ^1.1.5 => 1.2.1
    vite: ^2.3.3 => 2.3.3

Used package manager: yarn

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