handle case where git cli is missing in `dbt deps` (#396)
handle case where git cli is missing in `dbt deps` (#396)

* handle case when git cli is not installed. in addition, do not call exit directly, just raise RuntimeException
nave91/dbt,analyst-collective/dbt,analyst-collective/dbt,fishtown-analytics/dbt,nave91/dbt,fishtown-analytics/dbt,fishtown-analytics/dbt