refgene is a production requirement

[fabianegli]

refgene is now a production requirement.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[codecov]

Codecov Report

Merging #1756 (82937d1) into dev (a523f2e) will increase coverage by 0.06%.
The diff coverage is n/a.

❗ Current head 82937d1 differs from pull request most recent head 23b2828. Consider uploading reports for the commit 23b2828 to get more accurate results

@@            Coverage Diff             @@
##              dev    #1756      +/-   ##
==========================================
+ Coverage   68.46%   68.52%   +0.06%     
==========================================
  Files          59       59              
  Lines        7131     7152      +21     
==========================================
+ Hits         4882     4901      +19     
- Misses       2249     2251       +2     

Impacted Files	Coverage Δ
nf_core/modules/modules_json.py	73.27% <0.00%> (-0.10%)	⬇️
nf_core/__main__.py	52.66% <0.00%> (-0.02%)	⬇️
nf_core/modules/list.py	71.23% <0.00%> (ø)
nf_core/modules/update.py	75.37% <0.00%> (ø)
nf_core/modules/modules_repo.py	84.18% <0.00%> (+1.32%)	⬆️
nf_core/modules/install.py	72.36% <0.00%> (+2.80%)	⬆️

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