Bump dmutils version in requirements.txt
Bump dmutils version in requirements.txt

Feature flags is now in the master branch of dmutils, so we can
require a tagged version again instead of a specific branch.

alphagov/digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,mtekel/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend