add required dependencies (#3046)

Author: Le-Zheng

spark/dl/pom.xml

@@ -31,6 +31,11 @@
             <artifactId>imageio-jpeg</artifactId>
             <version>3.2.1</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.protobuf</groupId>
+            <artifactId>protobuf-java</artifactId>
+            <version>3.4.0</version>
+        </dependency>
         <dependency>
             <groupId>org.apache.hadoop</groupId>
             <artifactId>hadoop-client</artifactId>