Bump OpenTelemetry.Exporter.Zipkin from 1.5.1 to 1.6.0

Bumps [OpenTelemetry.Exporter.Zipkin](https://github.com/open-telemetry/opentelemetry-dotnet) from 1.5.1 to 1.6.0.
- [Release notes](https://github.com/open-telemetry/opentelemetry-dotnet/releases)
- [Commits](open-telemetry/opentelemetry-dotnet@core-1.5.1...core-1.6.0)

---
updated-dependencies:
- dependency-name: OpenTelemetry.Exporter.Zipkin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

src/Directory.Packages.props

@@ -17,7 +17,7 @@
     <PackageVersion Include="MongoDB.Driver.Core.Extensions.DiagnosticSources" Version="1.3.0" />
     <PackageVersion Include="OpenTelemetry.Exporter.OpenTelemetryProtocol.Logs" Version="1.5.0-rc.1" />
     <PackageVersion Include="OpenTelemetry.Exporter.Prometheus.HttpListener" Version="1.5.0-rc.1" />
-    <PackageVersion Include="OpenTelemetry.Exporter.Zipkin" Version="1.5.1" />
+    <PackageVersion Include="OpenTelemetry.Exporter.Zipkin" Version="1.6.0" />
     <PackageVersion Include="OpenTelemetry.Extensions.Propagators" Version="1.5.1" />
     <PackageVersion Include="OpenTelemetry.Instrumentation.AspNet" Version="1.0.0-rc9.9" />
     <PackageVersion Include="OpenTelemetry.Instrumentation.AspNetCore" Version="1.5.1-beta.1" />