fix: forced create symbolic link

[mikanIchinose]

Problem

pnpm demo:dev cannot recreate a symbolic link at ubuntu-18.04.

pnpm demo:dev

> @0.13.10 demo:dev /home/solenoid/ghq/github.com/mikanIchinose/slidev
> pnpm -C demo/starter run dev


> @ dev /home/solenoid/ghq/github.com/mikanIchinose/slidev/demo/starter
> ln -sF ../../packages/create-app/template/slides.md slides.md && nodemon -w '../../packages/slidev/dist/*.js' --exec 'slidev ./slides.md --open=false --log=info'

ln: failed to create symbolic link 'slides.md': File exists
 ERROR  Command failed with exit code 1.
 ERROR  Command failed with exit code 1.

Solution

add option -f at dev script of demo/starter/packege.json