fix compile error of streaming project

explicit return type for implicit function

Author: James Z.M. Gao <gaozhm@mediav.com>

Closes #153 from gzm55/work/streaming-compile and squashes the following commits:

11e9c8d [James Z.M. Gao] fix style error
fe88109 [James Z.M. Gao] fix compile error of streaming project

streaming/src/main/scala/org/apache/spark/streaming/api/java/JavaPairDStream.scala

@@ -737,7 +737,8 @@ class JavaPairDStream[K, V](val dstream: DStream[(K, V)])(
 }
 
 object JavaPairDStream {
-  implicit def fromPairDStream[K: ClassTag, V: ClassTag](dstream: DStream[(K, V)]) = {
+  implicit def fromPairDStream[K: ClassTag, V: ClassTag](dstream: DStream[(K, V)])
+  : JavaPairDStream[K, V] = {
     new JavaPairDStream[K, V](dstream)
   }