Fix dependency specification

[burnpanck]

• [x] Closes #188
• [x] Executed pre-commit run --all-files with no errors
• [x] The change is fully covered by automated unit tests
• [ ] ~Documented in docs/ as appropriate~
• [ ] ~Added an entry to the CHANGES file~

[andrewgsavage]

bors r+

[bors[bot]]

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