Update dependencies

[Nabushika]

Update all dependencies, including hyper to 1.4 and using thiserror instead of error-chain
Fix broken test
Make clippy happy

Closes #48
Closes #19

[Nabushika]

Tested this locally, all seems to be working!!

[sgrimee]

when fixing the test (thanks!) would it be possible to also adjust the comment so that it is consistent with the logic?
It says: "// invalid UUID (assumed base64) should return the event id"
It should say: "// invalid UUID (assumed base64) should return itself unmodified". Because it is not clear that it is the same as the event ID.