fix webcontent converter zip file error

test plan:
* import the package referenced in the ticket
* should not fail

fixes #CNVS-13425

Change-Id: I2663d4479824b90e80d7421f2e4ff6975f6731a6
Reviewed-on: https://gerrit.instructure.com/36588
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>