nit: get is not needed

Was there a reason for this get?
heh, [implicit `Long` to `LongWritable` in SparkContext](https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/SparkContext.scala#L1476), [wildcard `SparkContext` import](https://github.com/hammerlab/guacamole/blob/errant-get/src/main/scala/org/bdgenomics/guacamole/DistributedUtil.scala#L22)