shell.nix: add rust-analyzer for lsp

shell.nix

@@ -9,7 +9,7 @@ pkgs.stdenv.mkDerivation {
   buildInputs =
     with pkgs;
     with rustPlatform.rust;
-    [ rustc cargo pkg-config ] ++
+    [ rustc cargo rust-analyzer pkg-config ] ++
     default.ticker-update.buildInputs ++
     default.ticker-serve.buildInputs;