Update protoc-artifacts version to 2.6.1

Change-Id: I68755d6aa4f7bc831f4c3509ae26eb7ba1f39443

protoc-artifacts/pom.xml

@@ -10,7 +10,7 @@
   </parent>
   <groupId>com.google.protobuf</groupId>
   <artifactId>protoc</artifactId>
-  <version>3.0.0-alpha-3-pre</version>
+  <version>2.6.1</version>
   <packaging>pom</packaging>
   <name>Protobuf Compiler</name>
   <description>