Update git submodules
Update git submodules

* Update plugins/hooks from branch 'master'
  - Change docs links to actual file extension (.md)
    
    See https://gerrit-review.googlesource.com/83950 for detailed context.
    
    Change-Id: If9d4f0726a0d8d3ca66f01819eeada2b53ac41be
    
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