Remove non-ASCII character from README

There is a non-ASCII quote in the README file which causes problems with Berkshelf / Ridley.

/opt/chef/embedded/lib/ruby/gems/1.9.1/gems/json-1.8.1/lib/json/common.rb:155:in `encode': "\xE2" on US-ASCII (Encoding::InvalidByteSequenceError)

Easiest fix seems to be to just change the quote :)