Default the encoding to UTF-8 - needed when its not configured in the OS...

... or when using Ruby 1.9 rather than 2.0 (I believe).

This will be needed for our data.gov.uk setup and others may find it handy too. Otherwise jekyll fails on the curly quote marks in browse/by_topic/identifiers/uri-patterns/index.html

(sorry about the benign addition of the final carriage return in the file - vim does this automatically)