[SPARK-9960] [GRAPHX] sendMessage type fix in LabelPropagation.scala

Author: zc he <farseer90718@gmail.com>

Closes #8188 from farseer90718/farseer-patch-1.

graphx/src/main/scala/org/apache/spark/graphx/lib/LabelPropagation.scala

@@ -43,7 +43,7 @@ object LabelPropagation {
    */
   def run[VD, ED: ClassTag](graph: Graph[VD, ED], maxSteps: Int): Graph[VertexId, ED] = {
     val lpaGraph = graph.mapVertices { case (vid, _) => vid }
-    def sendMessage(e: EdgeTriplet[VertexId, ED]): Iterator[(VertexId, Map[VertexId, VertexId])] = {
+    def sendMessage(e: EdgeTriplet[VertexId, ED]): Iterator[(VertexId, Map[VertexId, Long])] = {
       Iterator((e.srcId, Map(e.dstAttr -> 1L)), (e.dstId, Map(e.srcAttr -> 1L)))
     }
     def mergeMessage(count1: Map[VertexId, Long], count2: Map[VertexId, Long])