content/quickstart: update Go metrics quickstart (#246)
content/quickstart: update Go metrics quickstart (#246)

Reported offline via email by Bala Chandrasekaran:
* Missing Name field for MLineLengthView which would
confusingly put metrics under "repl/*" instead of "demo/"

* Add `-v` to `go get` steps since installing packages for
the first time takes forever giving an impression of a
hanging installation. I've also added `-u` to ensure that
users always have the latest packages
census-instrumentation/opencensus-website,census-instrumentation/opencensus-website