Add "prepare" script so that emoji-mart can be installed from git.

package.json

@@ -77,7 +77,8 @@
     "prepublishOnly": "npm run build",
     "storybook": "start-storybook -p 6006",
     "build-storybook": "build-storybook",
-    "prettier": "prettier --write \"{src,scripts,spec}/**/*.js\""
+    "prettier": "prettier --write \"{src,scripts,spec}/**/*.js\"",
+    "prepare": "npm run build:dist"
   },
   "size-limit": [
     {