fix markduplicates tmp

[ggabernet]

Many thanks to contributing to nf-core/rnaseq!

To ensure that your build passes, please make sure your pull request is to the dev branch rather than to master. Thank you!

Please fill in the appropriate checklist below (delete whatever is not relevant). These are the most common things requested on pull requests (PRs).

PR checklist

• PR is to dev rather than master
• 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 necessary, also make a PR on the nf-core/rnaseq branch on the nf-core/test-datasets repo
• Ensure the test suite passes (nextflow run . -profile test,docker).
• Make sure your code lints (nf-core lint .).
• Documentation in docs is updated
• CHANGELOG.md is updated
• README.md is updated

Learn more about contributing: https://github.com/nf-core/rnaseq/tree/master/.github/CONTRIBUTING.md

[drpatelh]

Thanks @ggabernet !