Update index.md

Maybe I'm a fool, but the tag/branch release0.1 doesn't seem to exist when I try to clone.

  128 danking@beverly # git clone git@github.com:JuliaLang/julia.git -b 'release0.1' julia-0.1
  Cloning into 'julia-0.1'...
  Enter passphrase for key '/home/danking/.ssh/id_rsa': 
  fatal: Remote branch release0.1 not found in upstream origin

I, however, can check out the tag for v0.1.2. Is this the intended tag?