cant run dep ensure due to uber/jaeger-tracing no longer existing

[woodsaj]

running dep ensure no longer works as 'github.com/uber/jaeger-tracing' no longer exists.
see: golang/dep#1605

The repo as been moved to https://github.com/jaegertracing/jaeger-client-go

we need to update all imports to use the new import path

[woodsaj]

so, the repo has been moved but the import paths within the libs have not been updated. So the only way to tackle this is to modify Gopkg.toml to override the source address used for the packages.