neoflow_db.nf doesn't allow not outputting reference protein sequences

[zhuchcn]

noeflow_db.nf doesn't allow the -t flag of customProDBJ which allows not having reference protein sequences being output. I did a quick fix here and am happy to open a PR.

Btw, sorry that my text editor seems to trim off trailing spaces automatically so the the change looks more than it is.

https://github.com/zhuchcn/neoflow/compare/1c4f641..178fed6#diff-237f2dce2ee13cbc946bdefac8e3efe2b4bb93257576c8c0dc46f7098d5545c6