fix(docs): refer to Authorization header in the README, not Authentication

[ptabor]

The correct name of the header is 'Authorization' and not 'Authentication'.

Tested with:

curl -H "Authorization: bearer {edited}" -X POST -d " \
 { \
   \"query\": \"query { viewer { login }}\" \
 } \
" https://api.github.com/graphql

Previously:

$ curl -H "Authentication: bearer {edited}" -X POST -d " \
 { \
   \"query\": \"query { viewer { login }}\" \
 } \
" https://api.github.com/graphql
{
  "message": "This endpoint requires you to be authenticated.",
  "documentation_url": "https://docs.github.com/graphql/guides/forming-calls-with-graphql#authenticating-with-graphql"
}

[timrogers]

Great spot! Thanks for fixing this ❤️

[github-actions]

🎉 This PR is included in version 5.0.4 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

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