rust: Ensure toml-mode is installed

Ensure that the toml-mode is installed and enable it (needs taplo,
`cargo install taplo-cli --features lsp`).

.emacs.d/config/dev.el

@@ -38,5 +38,6 @@
 
 (use-package lsp-mode
   :ensure t
-  :config
-  (add-hook 'rust-mode-hook 'lsp-deferred))
+  :hook
+  (rust-mode . lsp-deferred)
+  (toml-mode . lsp-deferred))

.emacs.d/config/rust.el

@@ -11,3 +11,4 @@
   (setq rust-format-on-save t))
 
 (use-package flycheck-rust :ensure t)
+(use-package toml-mode :ensure t)