Remove the .txt suffix from tutor

The tutor file is loaded as .txt which can potentially spawn a
language server. Then the path is unset, but the LS remains active.
This can cause panics since updates are now submitted for a doc
with no path.

As a quick workaround we remove the extension which should avoid
detection.

Fixes #3730

book/src/usage.md

@@ -2,7 +2,7 @@
 
 (Currently not fully documented, see the [keymappings](./keymap.md) list for more.)
 
-See [tutor.txt](https://github.com/helix-editor/helix/blob/master/runtime/tutor.txt) (accessible via `hx --tutor` or `:tutor`) for a vimtutor-like introduction.
+See [tutor](https://github.com/helix-editor/helix/blob/master/runtime/tutor) (accessible via `hx --tutor` or `:tutor`) for a vimtutor-like introduction.
 
 ## Registers
 

helix-term/src/application.rs

@@ -157,7 +157,7 @@ impl Application {
         compositor.push(editor_view);
 
         if args.load_tutor {
-            let path = helix_loader::runtime_dir().join("tutor.txt");
+            let path = helix_loader::runtime_dir().join("tutor");
             editor.open(&path, Action::VerticalSplit)?;
             // Unset path to prevent accidentally saving to the original tutor file.
             doc_mut!(editor).set_path(None)?;

helix-term/src/commands/typed.rs

@@ -1147,7 +1147,7 @@ fn tutor(
         return Ok(());
     }
 
-    let path = helix_loader::runtime_dir().join("tutor.txt");
+    let path = helix_loader::runtime_dir().join("tutor");
     cx.editor.open(&path, Action::Replace)?;
     // Unset path to prevent accidentally saving to the original tutor file.
     doc_mut!(cx.editor).set_path(None)?;