Use scope=machine-overridable for clangd.path

This allows the setting to continue to be overridable per-workspace.

Fixes #64

package.json

@@ -91,7 +91,7 @@
                 "clangd.path": {
                     "type": "string",
                     "default": "clangd",
-                    "scope": "machine",
+                    "scope": "machine-overridable",
                     "description": "The path to clangd executable, e.g.: /usr/bin/clangd."
                 },
                 "clangd.arguments": {