v5.1.0

📚 PR:

• Bumped fastify
• Bump @types/node from 13.13.6 to 14.0.1 (#52)
• Bump simple-get from 3.1.0 to 4.0.0 (#53)
• Bump tsd from 0.11.0 to 0.12.0 (#55)
• (issue #54) add custom error instance handling, use fastify-error (#57)