Remove decorator from pinned reqs

[btjanaka]

Description

Forgot to remove the decorator package from the pinned requirements when we removed it from setup.py in #200

TODO

Questions

Status

• [x] I have read the guidelines in CONTRIBUTING.md.
• [x] I have formatted my code using yapf
• [x] I have tested my code by running pytest
• [x] I have linted my code with pylint
• [x] I have added a one-line description of my change to the changelog in HISTORY.md
  • Exclude
• [x] This PR is ready to go