vim.lsp.buf.formatting() mentioned in README is deprecated

In the README, there are some comments which mention vim.lsp.buf.formatting().
This seems to be deprecated: https://github.com/neovim/neovim/blob/9acb52c8f386ea0a026ba4e314e1294da66f8e79/runtime/doc/deprecated.txt#L279

so you may want to change that to vim.lsp.buf.format()
