Change tooltip to reflect correct Continuous Sync badge condition

I asked a question a week or ago clarifying the condition for receiving the Continuous Sync badge on Coderwall. I received a response from Andrew (https://twitter.com/teabass/status/410085515829202944) that said the 24 pull requests must be before Christmas. The way this is currently worded suggests to me that you'd also get Christmas and the remaining days of December to finish your pull requests. This PR changes the wording to make this consistent with my understanding for the English locale.