Update Gemfile

fix "unable to get certificate CRL"

link: ruby/openssl#949 (comment)

Author: a-gave

Gemfile

@@ -10,4 +10,5 @@ group :jekyll_plugins do
 end
 
 gem 'webrick'
-gem "jekyll-fetch", '~> 0.2.1'
+gem "jekyll-fetch", '~> 0.2.1'
+gem "openssl"