docs(example): fix go get url

[javierprovecho]

[minor] following the README you hit the following error:

 ~/go/src/github.com/uber/jaeger/examples/hotrod   master  go run ./main.go all
main.go:8:2: cannot find package "github.com/jaegertracing/jaeger/examples/hotrod/cmd" in any of:
        /Users/me/go/src/github.com/uber/jaeger/vendor/github.com/jaegertracing/jaeger/examples/hotrod/cmd (vendor tree)
        /usr/local/Cellar/go/1.9.2/libexec/src/github.com/jaegertracing/jaeger/examples/hotrod/cmd (from $GOROOT)
        /Users/me/go/src/github.com/jaegertracing/jaeger/examples/hotrod/cmd (from $GOPATH)

[black-adder]

thanks!

[coveralls]

Coverage remained the same at 100.0% when pulling 5a61602 on javierprovecho:patch-1 into 10d660f on jaegertracing:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 5a61602 on javierprovecho:patch-1 into 10d660f on jaegertracing:master.