Increment minor version to 2.13 to prepare for a new release.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=155003222

Author: emrekultursay

src/agent/internals/src/main/java/com/google/devtools/cdbg/debuglets/java/GcpDebugletVersion.java

@@ -31,7 +31,7 @@ public final class GcpDebugletVersion {
   /**
    * Minor version of the agent.
    */
-  public static final int MINOR_VERSION = 12;
+  public static final int MINOR_VERSION = 13;
 
   /**
    * Debugger agent version string in the format of MAJOR.MINOR.