buffet: Fixed command state spelling for "cancelled"

GCD spec apparently expects the command status to be spelled as
"cancelled". Fixed...

BUG=brillo:552
TEST=`FEATURES=test emerge-link buffet`

Change-Id: I11a848f2f29ca7d63ce95d130b2a84aa75ced7fd
Reviewed-on: https://chromium-review.googlesource.com/260028
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/commands/command_instance.h b/buffet/commands/command_instance.h
index b3bd2e0..45cf485 100644
--- a/buffet/commands/command_instance.h
+++ b/buffet/commands/command_instance.h
@@ -99,7 +99,7 @@
   static const char kStatusPaused[];
   static const char kStatusError[];
   static const char kStatusDone[];
-  static const char kStatusCanceled[];
+  static const char kStatusCancelled[];
   static const char kStatusAborted[];
   static const char kStatusExpired[];