(maint) Use git reset

Previously the vendor script used git checkout however this casued some issues
in the Yard gem.  This commit changes to use git reset which will achieve the
same result but force any changes without error.

Author: glennsarti

Rakefile

@@ -100,7 +100,7 @@ task :gem_revendor do
     sh "git clone #{vendor[:github_repo]} #{gem_dir}"
     Dir.chdir(gem_dir) do
       sh 'git fetch origin'
-      sh "git checkout #{vendor[:github_ref]}"
+      sh "git reset --hard #{vendor[:github_ref]}"
     end
 
     # Cleanup the gem directory...