Update prebuilt proto libraries for Dataflow to 2016-01-20 version

----Release Notes----
[]
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=112792425

Author: kennknowles

sdk/pom.xml

@@ -430,7 +430,7 @@
     <dependency>
       <groupId>com.google.cloud.dataflow</groupId>
       <artifactId>google-cloud-dataflow-java-proto-library-all</artifactId>
-      <version>0.4.151117</version>
+      <version>0.4.160120</version>
     </dependency>
 
     <dependency>