Bump github.com/opentracing/opentracing-go from 1.1.0 to 1.2.0

Bumps [github.com/opentracing/opentracing-go](https://github.com/opentracing/opentracing-go) from 1.1.0 to 1.2.0.
- [Release notes](https://github.com/opentracing/opentracing-go/releases)
- [Changelog](https://github.com/opentracing/opentracing-go/blob/master/CHANGELOG.md)
- [Commits](https://github.com/opentracing/opentracing-go/compare/v1.1.0...v1.2.0

)

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