Fix ChangeSubject's addInstanceNameInSubject option

Invert the condition to match the semantic name.

Change-Id: Id9421788917145dd0a1f8798d93d32029a152f0b
diff --git a/resources/com/google/gerrit/server/mail/ChangeSubject.soy b/resources/com/google/gerrit/server/mail/ChangeSubject.soy
index 62092ae..48ec9a2 100644
--- a/resources/com/google/gerrit/server/mail/ChangeSubject.soy
+++ b/resources/com/google/gerrit/server/mail/ChangeSubject.soy
@@ -26,7 +26,7 @@
  * @param addInstanceNameInSubject boolean
  */
 {template .ChangeSubject kind="text"}
-  {if $addInstanceNameInSubject}
+  {if not $addInstanceNameInSubject}
     Change in {$shortProjectName}[{$branch.shortName}]: {$change.shortSubject}
   {else}
     Change in {$instanceAndProjectName}[{$branch.shortName}]: {$change.shortSubject}