Fix Heroku deployment

[shahthepro]

If you made a contract change, make sure to complete the checklist below before merging it in master.

Refer to our documentation for more details about contract security best practices.

Contract change checklist:

• Code reviewed by 2 reviewers.
• Copy & paste code review security checklist below this checklist.
• Unit tests pass
• Slither tests pass with no warning
• Echidna tests pass if PR includes changes to OUSD contract (not automated, run manually on local)