Update underlying pygments

[nikitabobko]

#285

There are three commits in the PR (output of git log):

commit 1a4e502ee49c3fd93dae4abb171fea49f9d52561
Author:     Nikita Bobko 
AuthorDate: Wed Apr 15 17:15:15 2026 +0200
Commit:     Nikita Bobko 
CommitDate: Wed Apr 15 17:52:23 2026 +0200

    2/2 Update CHANGELOG
    
    https://github.com/pygments/pygments.rb/issues/285

commit 17459482e393c8538a40f3b23c2d3f4a2d5a2c83
Author:     Nikita Bobko 
AuthorDate: Wed Apr 15 17:14:38 2026 +0200
Commit:     Nikita Bobko 
CommitDate: Wed Apr 15 17:52:17 2026 +0200

    1/2 Update pygments to 2.20.0
    
    https://github.com/pygments/pygments.rb/issues/285
    
    This commit is a result of the following command:
    
        bundle exec rake vendor:update

commit c0994e5e56dd50c38bb255a365e6442a8b04b01f
Author:     Nikita Bobko 
AuthorDate: Wed Apr 15 17:37:57 2026 +0200
Commit:     Nikita Bobko 
CommitDate: Wed Apr 15 17:37:57 2026 +0200

    Update Rakefile to use pip3
    
    Otherwise, `bundle exec rake vendor:update` fails

I split them into separate commits to simplify the verification of the first commit which just a result of shell command.

[nikitabobko]

I noticed that bundle exec rake vendor:update doesn't produce determenistic results. Every time. E.g. vendor/pygments-main/pygments-2.20.0.dist-info/RECORD contains ../../../../../../../../../Users/bobko/Library/Caches/com.apple.python which is obviously only on my machine

You might wanna regenerate the commit yourself