fixes typo for CNVS-15738

Test plan:
- Ensure that " Better File Browsing" feature flag is enabled
- Select the course
- Click on Files from the left navigation panel
- Select Multiple files in the right hand pane
- Download Zip button is displayed in the top
- Verify hover over tool tip text on the button is' Download Zip'

Change-Id: I2ce5664a1dbf89e43d71de34116045692983df1c
Reviewed-on: https://gerrit.instructure.com/41861
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Matt Fairbourn <mfairbourn@instructure.com>