Update README.md

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README.md

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 <img src='http://kentonv.github.com/capnproto/images/infinity-times-faster.png' style='width:334px; height:306px; float: right;'>
 
 Cap'n Proto is an insanely fast data interchange format and capability-based RPC system. Think
-JSON, except binary. Or think [Protocol Buffers](http://protobuf.googlecode.com), except faster.
+JSON, except binary. Or think [Protocol Buffers](https://github.com/google/protobuf), except faster.
 In fact, in benchmarks, Cap'n Proto is INFINITY TIMES faster than Protocol Buffers.
 
 [Read more...](http://kentonv.github.com/capnproto/)