Make Greetings.GreetInfo inner class static

Change-Id: Ie3dbcbe80c0dc39c7ea3af5294162a071beab6c7
diff --git a/src/main/java/com/googlesource/gerrit/plugins/cookbook/Greetings.java b/src/main/java/com/googlesource/gerrit/plugins/cookbook/Greetings.java
index 5cb3053..f53b066 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/cookbook/Greetings.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/cookbook/Greetings.java
@@ -35,7 +35,7 @@
     return Response.ok(l);
   }
 
-  class GreetInfo {
+  static class GreetInfo {
     String message;
     String country;
     String href;