Fix links to Guava API docs (#2074)
Fix links to Guava API docs (#2074)

In #2060, I pointed to an old version of Guava that doesn't include classes that we expose. As a result, our Javadoc output contained broken links.

Guava v27.0-jre contains these classes, so pointing to that version prevents broken links.
googleapis/java-bigtable-hbase,sduskis/cloud-bigtable-client,googleapis/java-bigtable-hbase,googleapis/java-bigtable-hbase,sduskis/cloud-bigtable-client