while working in some larger repos, the .terraform dir might be missing
for one reason or another, terraform-ls will fail to start and return:
```
Failed to find project root, language server won't start
```
check if tf_dir is empty, if so, just return the dir of the file in
buffer.
Default `g:ale_disable_lsp` to a new mode `'auto'` by default. With this
setting applied, ALE will now check for the presence of nvim-lspconfig
and automatically turn off particular LSP linters if already configured
via nvim-lspconfig.
For users that do not use `nvim-lspconfig`, everything should work as
before.
Andreas Åkesson