Remove the whitespace between Array[Vid]] and (.

Also remove the whitespace after Array(. If you want a whitespace there, you need to add a whitespace to before the closing ) so they are symmetric. 

Also the way this is written right now is a little bit hard to understand, because _ ++ _ is a separate argument. Perhaps

    graph.mapReduceTriplets[Array[Vid]](
      mapFunc = et => Array((et.srcId, Array(et.dstId)), (et.dstId, Array(et.srcId))),
      reduceFunc = _ ++ _)