Add line in environment.yml for crisprcleanr

[LaurenceKuhl]

PR checklist

• [ ] This comment contains a description of changes (with reason).
• [ ] If you've fixed a bug or added code that should be tested, add tests!
• [ ] If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• [ ] If necessary, also make a PR on the nf-core/crisprseq branch on the nf-core/test-datasets repository.
• [ ] Make sure your code lints (nf-core pipelines lint).
• [ ] Ensure the test suite passes (nextflow run . -profile test,docker --outdir <OUTDIR>).
• [ ] Check for unexpected warnings in debug mode (nextflow run . -profile debug,test,docker --outdir <OUTDIR>).
• [ ] Usage Documentation in docs/usage.md is updated.
• [ ] Output Documentation in docs/output.md is updated.
• [ ] CHANGELOG.md is updated.
• [ ] README.md is updated (including new tool citations and authors/contributors).

[LaurenceKuhl]

i also wonder why the tests run in our screening tests + in the nf-core modules repo so i wonder if this change is needed and/or why a user had this error

[mirpedrol]

we are not testing with conda here, only on PRs to master, so we could check the conda tests. It could also be specific to the user who had this error, we should check on their environment.