add publish-beta task

Author: bgrins

deno.json

@@ -6,7 +6,8 @@
     "serve": "deno run --watch --allow-env --allow-net=unpkg.com,0.0.0.0 --allow-read=. demo/server.jsx",
     "test-npm": "npm install --prefix npm && npm test --prefix npm",
     "build": "deno task test && deno run --allow-env --allow-read --allow-write=. build.js && deno task test-npm",
-    "publish": "deno task build && cd npm && npm publish --access public"
+    "publish": "deno task build && cd npm && npm publish --access public",
+    "publish-beta": "deno task build && cd npm && npm publish --tag beta --access public"
   },
   "test": {
     "files": {