Appends output of fish command to the file on Format

[thatanjan]

I use fish as user shell. If fish has some output, then it gets append to the file when I format the file. This happens for all the files.
I have this setup to format code on save.

vim.cmd [[
augroup FormatAutogroup
  autocmd!
  autocmd BufWritePost * FormatWrite
  autocmd BufWritePre *.tsx,*.ts,*.jsx,*.js EslintFixAll
augroup END
]]

Note: EslintFixAll command doesn't cause this bug

Steps to reproduce

1. Add echo "test" to ~/.config/fish/config.fish
2. Now format any file with this plugin and you should see this.
   

Thanks in advance.

[thatanjan]

@mhartington please help