Update rna-seq.nf

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

Fixed the issue where the script would error out due to not finding precise string. Replaced the string as requested in issue 129.

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!
• [ ] Documentation in docs is updated
• [ ] Replace dag.png with the most recent CI pipeline integrated_pe artifact
• [ ] Replace software_versions_mqc.yaml with the most recent CI pipeline generateVersions artifact
• [ ] Replace software_references_mqc.yaml with the most recent CI pipeline generateVersions artifact
• CHANGELOG.md is updated
• [ ] README.md is updated
• [ ] LICENSE.md is updated with new contributors
• [ ] Docker images moved to production release and changed in pipeline
• [ ] Docker images used in the CI unit tests match those used in pipeline

• Close issue
  Closes #129 (closed)

/cc @ghenry @venkat.malladi