Add newer dictionary to cargo-spellcheck

[jdjaustin]

Summary of changes Changes introduced in this pull request:

• Add en_US.dic as a custom dictionary to Forest.

Reference issue to close (if applicable)

Closes issue #1726

Other information and links

[lemmih]

Good. Could you go through the words in forest.dic one-by-one and remove them if they appear in en_US.dic?

[elmattic]

You can remove words like blockchain from forest.dic (like David had suggested).

Also are we going to clean up a bit this dictionary? File is 1.72 MB large. ie.

blockchain
blockchain's
blockchains

could become:

blockchain/SM