Resolve Issues with Shipping  to Librato Metrics

Resolve Issues with Shipping Metrics to Librato

Resolves Issue:

`rearviewmirror.rb:77: undefined local variable or method 'queue' for main:Object (NameError)`

Code Changed: queue should be $queue when flushing queue to Librato metrics. Variable had been used globally initially (line 28) and then locally later (line 77).

Additional Code Change: made one change to Gemfile - using read-only git repository clone for Gem install.