Opening files via FZF results in relative line numbers being disabled, even when using the latest neovim

- Category
- [ ] Question
- [x] Bug
- [ ] Suggestion
- OS
- [x] Linux
- [ ] macOS
- [ ] Windows
- [ ] Etc.
- Vim
- [ ] Vim
- [x] Neovim

Using the latest version of neovim (0.2.1) it seems FZF still has some issues with disabling relative line numbers. To test this I used the following config:

```vimrc
set nocompatible hidden laststatus=2

if !filereadable('/tmp/plug.vim')
silent !curl --insecure -fLo /tmp/plug.vim
\ https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim
endif

source /tmp/plug.vim
call plug#begin('/tmp/plugged')
Plug 'junegunn/fzf', { 'do': './install --bin' }
Plug 'junegunn/fzf.vim'
call plug#end()

set number
set rnu

autocmd VimEnter * PlugClean! | PlugUpdate --sync
autocmd TermOpen * setlocal nonumber nornu
```

The TermOpen autocmd is present to disable line numbers for terminal windows. Using this config (or my actual config for that matter) will result in relative line numbers being disabled when opening a split via FZF. For example:

1. Go to a directory with a bunch of files
2. Open a file the normal way, observe how `rnu` is working
3. Type `:Files` and search for a file, then hit C-V to open a vertical split
4. Observe how `rnu` is disabled and instead we're left with just regular line numbers

This is using fzf.vim commit 4b9e2a03fe8389da852b0059bd7d0dfffd380956 and fzf commit 2cd0d4a9f7a0a0a86c1ee70da9fb970ec18eac50.