Merge pull request #6 from pathawks/variable_params

Merge pull request 6

Author: parkr

lib/jekyll-gist/gist_tag.rb

@@ -5,10 +5,10 @@ class GistTag < Liquid::Tag
       def render(context)
         if tag_contents = determine_arguments(@markup.strip)
           gist_id, filename = tag_contents[0], tag_contents[1]
-          if context[gist_id]
+          if context.has_key?(gist_id)
             gist_id = context[gist_id]
           end
-          if context[filename]
+          if context.has_key?(filename)
             filename = context[filename]
           end
           gist_script_tag(gist_id, filename)