v7.19.0 Add LIFF new properties and verification token API

What's Changed

• Make the X-Line-Signature header case-insensitive when handling in server side. by @cappyzawa in #331
• go mod tidy by @cappyzawa in #330
• Add liffApp properties by @clsung in #336
• feat(method): verify access token method by @blackhun11 in #338
• Update version to 7.19.0 by @kkdai in #339

New Contributors

• @cappyzawa made their first contribution in #331
• @blackhun11 made their first contribution in #338

Full Changelog: v7.18.0...v7.19.0