Japanese translations provided where missing for "rampup" levels

#Summary

Translated files for `rampup` levels into Japanese, where needed.

#Changes

This commit updates the following level files:

`cherryPick.js`
`detachedHead.js`
`relativeRefs2.js`
`relativeRefs.js`
`interactiveRebase.js`

This level had an existing Japanese translation, so it was skipped:

`reversingChanges.js`

No source code changes, or other changes were applied.

#Testing

`grunt fastBuild`
and
`grunt build`

passed with no errors.

Visual playthrough of all touched levels completed in browser.