Update worker container image for 2.0.0-beta4-SNAPSHOT

Signed-off-by: Jason Kuster <jasonkuster@google.com>

Author: jasonkuster

pom.xml

@@ -106,7 +106,7 @@
     <beam.version>0.6.0</beam.version>
 
     <dataflow.release_name>Google Cloud Dataflow SDK for Java</dataflow.release_name>
-    <dataflow.container_version>${project.version}-20170202</dataflow.container_version>
+    <dataflow.container_version>${project.version}-20170317</dataflow.container_version>
     <dataflow.environment_major_version>6</dataflow.environment_major_version>
   </properties>