[vscode] Workaround broken activation for .mv files

Suggested by Tomer Chachamu (thanks!) in
microsoft/vscode-discussions#901

Should fix issue #596 , however I'm not marking this as closed, as
this workaround could actually be due to a VSCode bug.

Thanks to Théo Zimmerman for the report.

CHANGES.md

@@ -10,6 +10,9 @@
  - fix hover position computation on the presence of Utf characters
    (@ejgallego, #597, thanks to Pierre Courtieu for the report and
    example, closes #594)
+ - workaround seemingly VSCode activation bug that prevented extension
+   activation (@ejgallego @r3m0t, #598, cc #596, reported by Théo
+   Zimmerman)
 
 # coq-lsp 0.1.8: Trick-or-treat
 -------------------------------

editor/code/package.json

@@ -28,6 +28,9 @@
     "type": "git",
     "url": "https://github.com/ejgallego/coq-lsp"
   },
+  "activationEvents": [
+    "onLanguage:markdown"
+  ],
   "contributes": {
     "languages": [
       {