Replace deprecated `raven-go` and `logrus_sentry` with `sentry-go`

`raven-go` and `logrus_sentry` are both deprecated. The Sentry team archived `raven-go` in favor of `sentry-go`, and `logrus_sentry` depends on it.

Both are only used in `main.go`. `sentry-go` has a built-in logrus hook (`sentry-go/logrus`) so the swap is pretty contained. This also drops the transitive `certifi/gocertifi` dependency.