Fix documentation reference.

[jumper149]

I was trying to build it with nix and it threw an error. Was an easy fix though :)

It works now so I think this can be merged.

---

My nix expression for reference:

(super.vimUtils.buildVimPluginFrom2Nix {
  pname = "idris2";
  version = "2021-12-09";
  src = super.fetchFromGitHub {
    owner = "jumper149";
    repo = "idris2-nvim";
    rev = "e077ca5c3bd2d0f26c758440e21e77262ead52b1";
    sha256 = "SIrN4cgQfD8VPZxjmbypAFN3Z4NomMwNlzxQLoe2wng=";
  };
})

---

This was the error message:

Sourcing vim-gen-doc-hook
unpacking sources
unpacking source archive /nix/store/mvgkl3ml9j186xk6czdsnf2h3v2yg0nr-source
source root is source
patching sources
configuring
building
installing
post-installation fixup
Executing vimPluginGenTags
Building help tags
Error detected while processing command line:
E154: Duplicate tag "idris2.metavars.goto_next()" in file /nix/store/n2py47hfq6s3y7xvgisljsn0pchqdhb5-vimplugin-idris2-2021-12-09/./doc/idris2-nvim.txtFailed to build help tags!
error: builder for '/nix/store/7ilbxknk7zisi1fifrivna2vdlh0c50b-vimplugin-idris2-2021-12-09.drv' failed with exit code 1;
       last 10 log lines:
       > source root is source
       > patching sources
       > configuring
       > building
       > installing
       > post-installation fixup
       > Executing vimPluginGenTags
       > Building help tags
       > Error detected while processing command line:
       > E154: Duplicate tag "idris2.metavars.goto_next()" in file /nix/store/n2py47hfq6s3y7xvgisljsn0pchqdhb5-vimplugin-idris2-2021-12-09/./doc/idris2-nvim.txtFailed to build help tags!