docs: Fix spelling errors in upgrade guide

[TastefulElk]

Hey and congrats on the v2 launch! 🥳 I found a couple of spelling errors in the upgrade guide when I was going through it.

[bboure]

Thanks! That's all me: typos :)

side note: I recently found this plugin to help me with this

[github-actions[bot]]

:tada: This PR is included in version 2.1.0 :tada:

The release is available on:

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

Your semantic-release bot :package::rocket: