Update links for discord and code of conduct

[colinkey]

Purpose

Updates documentation to close #1631 and #1632

Description

For #1631, searched through the codebase to update almost all references from the discord to the luckyframework.com/chat link. The only unchanged reference is the badge in the README.

For #1632, updated the contributing guidelines to remove the reference to the thoughtbot code of conduct as well as making a few updates to urls that while still worked, pointed to an outdated repo name.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[matthewmcgarvey]

Cool 🎉

[edwardloveall]

Thanks @colinkey!

[jwoertink]

Nice! Thanks so much for doing this