Replace read-only empty hash with private constant (#418)
Replace read-only empty hash with private constant (#418)

Merge pull request 418
benbalter/jekyll-seo-tag,jekyll/jekyll-seo-tag,jekyll/jekyll-seo-tag,jekyll/jekyll-seo-tag,benbalter/jekyll-seo-tag,benbalter/jekyll-seo-tag