`hub` now requires Go 1.3 or better to compile

Due to some breaking changes in Go's standard library which we need,
e.g., https://code.google.com/p/go/source/diff?spec=svn733fefb1deae5490f2d6fcf498667a9077f92a42&r=733fefb1deae5490f2d6fcf498667a9077f92a42&format=side&path=/src/pkg/net/http/transport.go