Fixes cli error for Asciidoctor

[pre-martin]

The original fix for #8676 introduced illegal arguments for Asciidoctor, causing no rendering at all. This PR fixes the command line arguments so that Asciidoctor properly renders the text. See https://asciidoctor.org/docs/user-manual/#piping-content-through-the-cli as reference.

[codecov-commenter]

Codecov Report

Merging #12677 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #12677      +/-   ##
==========================================
- Coverage   43.32%   43.31%   -0.01%     
==========================================
  Files         646      646              
  Lines       71592    71592              
==========================================
- Hits        31015    31010       -5     
- Misses      35565    35569       +4     
- Partials     5012     5013       +1     

Impacted Files	Coverage Δ
modules/util/timer.go	42.85% <0.00%> (-42.86%)	⬇️
modules/indexer/stats/queue.go	52.94% <0.00%> (-11.77%)	⬇️
modules/notification/mail/mail.go	34.48% <0.00%> (-3.45%)	⬇️
modules/notification/ui/ui.go	80.55% <0.00%> (-2.78%)	⬇️
modules/process/manager.go	72.50% <0.00%> (-2.50%)	⬇️
modules/queue/workerpool.go	58.77% <0.00%> (-1.23%)	⬇️
models/notification.go	66.13% <0.00%> (-0.92%)	⬇️
models/error.go	35.32% <0.00%> (-0.35%)	⬇️
models/issue_comment.go	53.90% <0.00%> (+0.15%)	⬆️
services/pull/pull.go	42.26% <0.00%> (+0.23%)	⬆️
... and 5 more

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