Default Coco/R validator to GNU-grammar/bin/GM2

Phase 2 wiring: point modula2.cocoR.validatorCommand at the tested
Coco/R validator so diagnostics work out of the box on this machine.

extensions/modula2-language/package.json

@@ -72,7 +72,7 @@
         },
         "modula2.cocoR.validatorCommand": {
           "type": "string",
-          "default": "",
+          "default": "/home/eric/Projets/Projets-Modula2/MyWork/Theia/GNU-grammar/bin/GM2",
           "description": "Executable that validates a Modula-2 source file using the generated Coco/R parser. Leave empty to disable Coco/R diagnostics."
         },
         "modula2.cocoR.validatorArguments": {