[paste] Fixed key path according to new response schema

[viperadnan-git]

Recently https://pasting.ga updated their API which returns the key in JSON format.

• Response before

  Ufbto5NU

• Response now

  {
  "key": "Ufbto5NU",
  "url": "http://zsrs08.deta.dev/Ufbto5NU"
  }

[rking32]

Thanks