Fix website scala doc

[zachgk]

Description

Fix for Scala doc building on website for older versions

I tested this with ./build_all_version.sh "mxdoc;v1.3.x;v1.2.0;v1.1.0;v1.0.0;v0.12.0;v0.11.0" "mxdoc;1.3.1;1.2.1;1.1.0;1.0.0;0.12.1;0.11.0" https://github.com/zachgk/incubator-mxnet.git

@aaronmarkham @lanking520

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[vandanavk]

@mxnet-label-bot add [pr-awaiting-review, Scala, Doc]