[FIX] Fixed wrong Sentinel FQCN.

Hey mate,

I noticed just now that when I pushed PR #94, I had previously tested changing my `vendor/` files. When I forked, however, I did the edits by hand, and I didn't noticed that I typed the wrong Sentinel FQCN, which is a bit confusing since it's different than Sentry way.

My apologies for not having noticed this before. I was updating my `vendor/` with upstream right now and I just realized it suddenly stopped to work. So I've found my fault.

This fixes the mistake. Apologies for the inconvenience!