That looks like it *could* solve the issue, however this doesn't print the quotes.
Assuming you have a category about ruby, the printed YAML should be: `category: "Ruby"` currently it would print `category: Ruby`, without the quotes.

I am unsure whether Jekyll will interpret that correctly. If it does, then that should be fine, if it doesn't, you have to add the quotes in explicitly. I haven't tested this code, I'm unsure it Ruby will correctly interpret the nested quotes.

    category = ENV["category"] ? "\"#{ENV["category"].gsub(/-/, ' ')}\"" : ""