fix: move source-map to dependencies

[lukashass]

I'm using @intlify/vite-plugin-vue-i18n with yarn 2.

When starting vite I get:

Error: @intlify/cli tried to access source-map, but it isn't declared in its dependencies; this makes the require call ambiguous and unsound.

Required package: source-map (via "source-map")
Required by: @intlify/cli@npm:0.2.0 (via ./.yarn/cache/@intlify-cli-npm-0.2.0-11f1d4a30e-f709484da4.zip/node_modules/@intlify/cli/lib/src/generator/)

My workaround for now is adding the following to .yarnrc.yml

packageExtensions:
  "@intlify/cli@0.2.0":
    dependencies:
      source-map: "*"

It would certainly be nice if that wouldn't be necessary 😉
Hence this PR.

[kazupon]

Thanks!