[geary] Fix code attribute to compile under Vala 0.28: Bug #741760

[Jim Nelson <jnelson src gnome org>]

commit abe45d51b45a8e50ec6b97a836c55a295da8246d
Author: Jim Nelson <jim yorba org>
Date:   Fri Dec 19 12:54:43 2014 -0800

    Fix code attribute to compile under Vala 0.28: Bug #741760

 src/engine/imap-db/imap-db-gc.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/engine/imap-db/imap-db-gc.vala b/src/engine/imap-db/imap-db-gc.vala
index 0dae3ae..c2a2860 100644
--- a/src/engine/imap-db/imap-db-gc.vala
+++ b/src/engine/imap-db/imap-db-gc.vala
@@ -54,7 +54,7 @@ private class Geary.ImapDB.GC {
     /**
      * Operation(s) recommended by { link should_run_async}.
      */
-    [Flag]
+    [Flags]
     public enum RecommendedOperation {
         /**
          * Indicates no garbage collection is recommended at this time.