Add R label to languageLabels.json

Author: webholik

lib/assets/languageLabels.json

@@ -18,5 +18,6 @@
   "nodejs": "NodeJs",
   "ocaml": "OCaml",
   "shell": "Shell",
-  "dart": "Dart"
+  "dart": "Dart",
+  "r": "R"
 }