Temporarily disable "@sleepdiary/core" dependency

The build script wants to download this from a public repository.
This commit can be reverted once that package goes live.

See sleepdiary/core#1

package.json

@@ -13,7 +13,6 @@
     "lint": "vue-cli-service lint"
   },
   "dependencies": {
-    "@sleepdiary/core": "^0.1.0",
     "core-js": "^3.6.5",
     "vue": "^2.6.11",
     "vue-router": "^3.2.0",