fix(doc): link to CommandLine.java

[simon04]

When viewing https://picocli.info/, the link resolves to the non-existing https://picocli.info/src/main/java/picocli/CommandLine.java

[codecov-io]

Codecov Report

Merging #553 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #553   +/-   ##
=========================================
  Coverage     89.17%   89.17%           
  Complexity      285      285           
=========================================
  Files             4        4           
  Lines          3946     3946           
  Branches        967      967           
=========================================
  Hits           3519     3519           
  Misses          213      213           
  Partials        214      214

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[remkop]

Thank you for the pull request!
I merged it into master. Will update the link in the generated HTML when I get home.

[remkop]

Finally updated the generated HTML as well... Sorry for the delay.