Fix yarn link breaks jest
What does this MR do?
When using yarn link to test gitlab-ui locally, jest tests will fail
if any of the files include @gitlab/ui because jest can't find
them.
This updates moduleDirectories to include <rootDir> when running
locally as per this jest issue:
https://github.com/facebook/jest/issues/2447#issuecomment-454748972
Screenshots
n/a
Edited by Paul Slaughter