adjust cors.rb file to match heroku FE url

[SethPerna]

Is this a fix or a feature?

• [x] Bug fix
• [ ] Feature
• [ ] Refactor

Describe the feature - fix - refactor:

remove slash from FE URL in cors.rb for heroku, to hopefully solve cors issues

How was this tested?

• [ ] open index.html
• [ ] localhost
• [ ] terminal

Where should the reviewer start - test:

Additional comments: