PluginVelocityRuntimeProvider: Fix warning flagged by error prone

Change-Id: I68b216538bcbbbb07b33e9a7282312e27f56cd57

github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/PluginVelocityRuntimeProvider.java

diff --git a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/PluginVelocityRuntimeProvider.java b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/PluginVelocityRuntimeProvider.java
index d0080c5..3e60433 100644
--- a/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/PluginVelocityRuntimeProvider.java
+++ b/github-plugin/src/main/java/com/googlesource/gerrit/plugins/github/velocity/PluginVelocityRuntimeProvider.java
@@ -21,6 +21,7 @@
 import com.google.inject.Singleton;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.Arrays;
 import java.util.Properties;
 import org.apache.velocity.runtime.RuntimeConstants;
 import org.apache.velocity.runtime.RuntimeInstance;
@@ -92,7 +93,7 @@
         "Cannot find any Jar file in "
             + pluginName
             + " plugin class loader URLs "
-            + jarUrls
+            + Arrays.toString(jarUrls)
             + ": unable to initialize Velocity resource loading.");
   }
 }