Fix: Show copy buttons in code blocks (#1198)

[deining]

After updating to latest asciidoctor gradle plugin (#1202), copy buttons in code blocks were not displayed any more.
This is corrected with this PR.

[codecov-io]

Codecov Report

Merging #1208 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1208      +/-   ##
============================================
- Coverage     94.32%   94.30%   -0.02%     
  Complexity      455      455              
============================================
  Files             2        2              
  Lines          6663     6676      +13     
  Branches       1793     1795       +2     
============================================
+ Hits           6285     6296      +11     
- Misses          101      102       +1     
- Partials        277      278       +1     

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/picocli/CommandLine.java	94.14% <0.00%> (-0.02%)	314.00% <0.00%> (ø%)

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[remkop]

Merged and published the rendered HTML.
Thank you for the contribution!