Bump ddtrace from 0.51.0 to 0.51.1

Bumps [ddtrace](https://github.com/DataDog/dd-trace-rb) from 0.51.0 to 0.51.1.
- [Release notes](https://github.com/DataDog/dd-trace-rb/releases)
- [Changelog](https://github.com/DataDog/dd-trace-rb/blob/v0.51.1/CHANGELOG.md)
- [Commits](https://github.com/DataDog/dd-trace-rb/compare/v0.51.0...v0.51.1)

---
updated-dependencies:
- dependency-name: ddtrace
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -229,7 +229,7 @@ GEM
       activerecord (>= 5.a)
       database_cleaner-core (~> 2.0.0)
     database_cleaner-core (2.0.1)
-    ddtrace (0.51.0)
+    ddtrace (0.51.1)
       ffi (~> 1.0)
       msgpack
     debugger-linecache (1.2.0)