Fixed thread safety issue with RandomGenerator
Fixed thread safety issue with RandomGenerator

The Random class is not thread safe, however it was called from
static methods that may be invoked by multiple threads.

bilal-fazlani/statsd-csharp-client,DarrellMozingo/statsd-csharp-client,goncalopereira/statsd-csharp-client,Kyle2123/statsd-csharp-client,agileharbor/telegraf-client,Pereingo/statsd-csharp-client,circleback/statsd-csharp-client