Fix lab extension build.

Author: T4rk1n

@plotly/dash-jupyterlab/package.json

@@ -26,7 +26,7 @@
   "scripts": {
     "build": "tsc",
     "build:pack": "jlpm run prepare && jlpm pack --filename ../../dash/labextension/dist/dash-jupyterlab.tgz && jlpm run build:copy",
-    "build:copy": "cp package.json ../../dash/labextension/dist/dash-jupyterlab.tgz",
+    "build:copy": "cp package.json ../../dash/labextension/dist/package.json",
     "clean": "rimraf lib",
     "prepare": "mkdir -p ../../dash/labextension/dist && jlpm run clean && jlpm run build",
     "prettier": "prettier --write '{!(package),src/**,!(lib)/**}{.js,.jsx,.ts,.tsx,.css,.json,.md}'",

MANIFEST.in

@@ -10,3 +10,5 @@ include dash/html/*
 include dash/dash_table/*
 include dash/dash-renderer/build/*.js
 include dash/dash-renderer/build/*.map
+include dash/labextension/dist/dash-jupyterlab.tgz
+include dash/labextension/package.json