Fix directory argument with --git-recurse

[EricFromCanada]

Description

Need to include the directory when passing back the list of Markdown files.

Before:

$ mdl -v -g Homebrew
Loaded config from /usr/local/Homebrew/.mdlrc
Checking README.md...
/usr/local/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.8/lib/ruby/gems/2.6.0/gems/mdl-0.11.0/lib/mdl/doc.rb:50:in `read': No such file or directory @ rb_sysopen - README.md (Errno::ENOENT)

After:

$ mdl -v -g Homebrew
Loaded config from /usr/local/Homebrew/.mdlrc
Checking Homebrew/README.md...
Processing rule MD001
Processing rule MD002
...

Related Issues

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (non-breaking change that does not add functionality but updates documentation)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• Wrote good commit messages
• Feature branch is up-to-date with master, if not - rebase it
• Added tests for all new/changed functionality, including tests for positive and negative scenarios
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences

[jaymzh]

Nice catch, thanks! Small nit.