google-cloud-logging LogEntry is missing a "spanId" field.

[sebright]

I'm writing a LoggingEnhancer for OpenCensus (census-instrumentation/opencensus-java#1212). I noticed that the Stackdriver LogEntry has a "spanId" field in https://cloud.google.com/logging/docs/reference/v2/rest/v2/LogEntry, but the google-cloud-logging LogEntry class does not (LogEntry.java). Should both LogEntry data structures have a "spanId"? If so, I can make a pull request to add the field.

/cc @g-easy

[yihanzhen]

That sounds quite reasonable to me. Please feel free to send over pull requests.
(I don't know a lot about logging so @garrettjonesgoogle @pongad please share your inputs if you see a problem here)

[sebright]

Thanks! I made a PR: #3332