Update normalize.css to v2.1.2 and minify
Add update_normalize_css task
Remove duplicate
Fix TypeError on Generation

After several page build fails, this seems to have fixed up the following error:

lib/jekyll/excerpt.rb:108:in `partition': type mismatch: NilClass given (TypeError)
Merge pull request #1430 from penibelst/site-speed

Update normalize.css to v2.1.2 and minify
Update history to reflect the merge of #1430