Update DiffEngine.slnx

Author: SimonCropp

src/DiffEngine.slnx

@@ -8,7 +8,7 @@
     <File Path="../appveyor.yml" />
     <File Path="../claude.md" />
     <File Path="../readme.source.md" />
-    <File Path=".editorconfig" />
+    <File Path="../.editorconfig" />
     <File Path="Directory.Build.props" />
     <File Path="Directory.Packages.props" />
     <File Path="global.json" />