Add denops/supported_versions.json

cf. vim-denops/denops.vim#396

Author: kg8m

denops/supported_versions.json

@@ -0,0 +1,5 @@
+{
+  "deno": "1.45.0",
+  "vim": "9.0.1499",
+  "neovim": "0.8.0"
+}