FIX: keys returns an array not a string

FIX: keys returns an array not a string

Followup to 88e26b26

diff --git a/plugin.rb b/plugin.rb
index 3aab315..06017c3 100644
--- a/plugin.rb
+++ b/plugin.rb
@@ -562,7 +562,7 @@ after_initialize do
         next if !post_revision.modifications.present?
 
         # do no notify recipients when only updating tags
-        next if post_revision.modifications.keys == 'tags'
+        next if post_revision.modifications.keys == ['tags']
 
         ids = []
         post = post_revision.post

GitHub sha: a6473575