Use newer hunspell dictionary.

[lemmih]

Issue summary

cargo-spellcheck ships with a builtin dictionary. Unfortunately, this dictionary is old and is missing a lot of words that are available in newer dictionaries.

Add en_US.dic as a custom dictionary to Forest.

Other information and links

[LesnyRumcajs]

Maybe we could propose (but not wait for reaction/new release/etc) this dictionary directly to the repo https://github.com/drahnr/cargo-spellcheck/tree/master/hunspell-data.