Change the artifact version to alpha-2.

Change-Id: Icef582d14170e24fa1707724be1aec1cc71d0948

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>3.0.0-alpha-2</version>
   <packaging>pom</packaging>
   <name>Protobuf Compiler</name>
   <description>