HOTFIX: Fixing test error in maven for flume-sink.

We needed to add an explicit dependency on scalatest since this
module will not get it from spark core like others do.

Author: pwendell

external/flume-sink/pom.xml

@@ -67,7 +67,10 @@
     <dependency>
       <groupId>org.scala-lang</groupId>
       <artifactId>scala-library</artifactId>
-      <version>2.10.4</version>
+    </dependency>
+    <dependency>
+      <groupId>org.scalatest</groupId>
+      <artifactId>scalatest_${scala.binary.version}</artifactId>
     </dependency>
   </dependencies>
   <build>