Microsoft has been talking about buying GitHub, a startup at the center of the software world last valued at $2 billion

Update: Microsoft on Monday officially announced the deal: it is buying GitHub for $7.5 billion in an all-stock deal.On Friday, Business Insider reported that Microsoft was in talks to buy GitHub, people close to the companies told us.The companies have had on-and-off conversations over the years, but talks grew more serious in the past few weeks, these people said.It's a change of course from ju