fix typo in build files (jeager)

[pjfanning]

Before submitting pull request:

• [x] Check if the project compiles by running sbt compile
• [x] Verify docs compilation by running sbt compileDocs
• [ ] Check if tests pass by running sbt test
• [x] Format code by running sbt scalafmt

The 3 mappings for mdocs - I searched the repo and found no uses of the 3 that are removed in this PR.

[adamw]

Thanks :)