Fix compilation error against Gerrit master

The return type of GerritWorkQueue.createQueue() has changed, forcing us
to change our implementation of ExecutorProvider

Change-Id: I81cbf237dba747d77250c4bbb53db0c6c7dfab05
Signed-off-by: Dariusz Luksza <dluksza@collab.net>
diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
index dd3be4c..0a0cfea 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/ExecutorProvider.java
@@ -17,11 +17,11 @@
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.server.git.WorkQueue;
 import com.google.inject.Provider;
-import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ScheduledExecutorService;
 
 public abstract class ExecutorProvider
-    implements Provider<ScheduledThreadPoolExecutor>, LifecycleListener {
-  private ScheduledThreadPoolExecutor executor;
+    implements Provider<ScheduledExecutorService>, LifecycleListener {
+  private ScheduledExecutorService executor;
 
   protected ExecutorProvider(WorkQueue workQueue, int threadPoolSize, String threadNamePrefix) {
     executor = workQueue.createQueue(threadPoolSize, threadNamePrefix);
@@ -39,7 +39,7 @@
   }
 
   @Override
-  public ScheduledThreadPoolExecutor get() {
+  public ScheduledExecutorService get() {
     return executor;
   }
 }