Scrooge updated to match plugin version

When I tried running scrooge I got to an error:
```
[error] (zipkin-scrooge/*:update) sbt.ResolveException: download failed: com.twitter#scrooge-runtime_2.9.2;3.12.2!scrooge-runtime_2.9.2.jar(doc)
[error] download failed: com.twitter#scrooge-runtime_2.9.2;3.12.2!scrooge-runtime_2.9.2.pom
[error] download failed: com.twitter#scrooge-runtime_2.9.2;3.12.2!scrooge-runtime_2.9.2.jar(src)
```
Updating scrooge dependency version to 3.12.3, so that it matches scrooge-plugin version, resolved the issue.