$FZF_DEFAULT_OPTS stopped working

- [x] I have read through https://github.com/junegunn/fzf.vim/blob/master/README.md
- [x] I have read through https://github.com/junegunn/fzf/blob/master/README-VIM.md
- [x] I have read through the manual page of fzf (`man fzf`)
- [x] I have searched through the existing issues

So, I just updated `fzf` and `fzf.vim`, and suddenly `$FZF_DEFAULT_OPTS` in my `init.vim` stops working. I don't know what happened previously it was working just fine.

Here is my config for `fzf.vim`
```vim
let $FZF_DEFAULT_OPTS="--color=dark --layout=reverse --margin=1,1 --color=fg:15,bg:-1,hl:1,fg+:#ffffff,bg+:0,hl+:1 --color=info:0,pointer:12,marker:4,spinner:11,header:-1"

let $FZF_DEFAULT_COMMAND="git ls-files --cached --others --exclude-standard || fd --type f --type l --hidden --follow"

command! -bang -nargs=? -complete=dir Files
\ call fzf#vim#files(, { 'options': "--prompt '⯈ '"}, 0)

let g:fzf_layout = { 'window': { 'width': 0.4, 'height': 0.25, 'yoffset': 0 } }
let g:fzf_preview_window = ''
let g:fzf_buffers_jump = 1

function! FZFOpen(command_str)
if (expand('%') =~# 'NERD_tree' && winnr('$') > 1)
exe "normal! \\"
endif
exe 'normal! ' . a:command_str . "\"
endfunction

nnoremap :call FZFOpen(':Files')
```
#### Screenshot

Previously It looked like this:
**env**
nvim: 0.4.3
fzf: 0.21.1
fzf.vim: 2115caeba1b55040bfdb1b8c38a836ad4e0b7669

Now:
**env**
nvim: 0.4.4
fzf: 0.22.0
fzf.vim: 4145f53f3d343c389ff974b1f1a68eeb39fba18b

Not a single command i.e. `:Buffers`,`:Tags`,`:Files` is respecting the `$FZF_DEFAULT_OPTS` inside `nvim`.

Also the same `FZF_DEFAULT_OPTS` is working fine in the terminal.

**Edit:**
I thought this https://github.com/junegunn/fzf.vim/issues/1089#issuecomment-673512649 was the issue but I seems like this issue is still there when using different themes i.e. [gruvbox-material](https://github.com/sainnhe/gruvbox-material) and other themes.