API doc links are broken

[igorbernstein2]

For example:

• bigtable's readme has: https://googleapis.github.io/google-cloud-java/google-cloud-clients/apidocs/index.html?com/google/cloud/bigtable/package-summary.html
• spanner's readme has: https://googleapis.github.io/google-cloud-java/google-cloud-clients/apidocs/index.html?com/google/cloud/spanner/package-summary.html

Both lead to a 404

[chingor13]

We had a bad docs build. This should now be fixed.