Build error bigtable/spark/build.sbt

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**The issue you're having must be related to a file in this repository.** We are unable to provide assistance for issues unrelated to samples in this repository.

Please include as much information as possible:

## In which file did you encounter the issue?
bigtable/spark/build.sbt

## Did you change the file? If so, how?
No

## Describe the issue
`sbt clean assembly` fails to build the uber jar
```
[error] lmcoursier.internal.shaded.coursier.error.FetchError$DownloadingArtifacts: Error fetching artifacts:
[error] https://repo1.maven.org/maven2/org/apache/avro/avro-mapred/1.11.0/avro-mapred-1.11.0-hadoop2.jar: not found: https://repo1.maven.org/maven2/org/apache/avro/avro-mapred/1.11.0/avro-mapred-1.11.0-hadoop2.jar
```

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