fix(@cubejs-client/playground): prepublishOnly for exports (#1171)

Author: RusovDmitriy

packages/cubejs-playground/package.json

@@ -54,7 +54,7 @@
     "build": "SKIP_PREFLIGHT_CHECK=true EXTEND_ESLINT=true react-app-rewired --max-old-space-size=3072 build && rm -Rf ../cubejs-server-core/playground/** && cp -R build/ ../cubejs-server-core/playground/",
     "eject": "SKIP_PREFLIGHT_CHECK=true EXTEND_ESLINT=true react-scripts eject",
     "lint": "eslint src/*.js src/*.jsx",
-    "prepublish": "babel src -d dist --copy-files"
+    "prepublishOnly": "babel src -d dist --copy-files"
   },
   "browserslist": [
     ">0.2%",