Make Module$ThreadPool public so it can be referenced

Change-Id: I6017793a72f9f72e26c014b5ad028ccbae25b123

src/main/java/com/googlesource/gerrit/plugins/reviewers/Module.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/reviewers/Module.java b/src/main/java/com/googlesource/gerrit/plugins/reviewers/Module.java
index 3ae0355..cc53853 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/reviewers/Module.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/reviewers/Module.java
@@ -38,7 +38,7 @@
 import com.googlesource.gerrit.plugins.reviewers.config.GlobalConfig;
 
 public class Module extends FactoryModule {
-  enum ThreadPool {
+  public enum ThreadPool {
     DIRECT,
     WORK_QUEUE,
     FAN_OUT