shell.nix: Use nixpkgs' rust-analyzer

See issue linked in the comment; this is more stable.

shell.nix

@@ -8,10 +8,9 @@ with pkgs;
 
 mkShell {
   buildInputs = [
-    rustChannel.rust
+    rust-analyzer # the one from Mozilla is slightly broken https://github.com/mozilla/nixpkgs-mozilla/issues/238
+    (pkgs.latest.rustChannels.stable.rust.override {
+      # extensions = ["rust-src"]; # unneeded because we're using rust-analyzer from nixpkgs
+    })
   ];
-
-  shellHook = ''
-    export RUST_SRC_PATH="${rustChannel.rust-src}/lib/rustlib/src/rust/library"
-  '';
 }