Fixed handlign the default retention policy

Rakefile

@@ -17,13 +17,15 @@ desc 'Sets up the retention policies'
 task :policies do
   db = ENV.fetch('INFLUX_DATABASE')
-  existing = CLIENT.list_retention_policies(db).map { |h| h['name'] }
-  unless existing.include?('default')
-    CLIENT.create_retention_policy('default', db, '1h', 1, true)
+  policies = CLIENT.list_retention_policies(db)
+  policy_names = policies.map { |h| h['name'] }
+  default = policies.find { |h| h['name'] == 'default' }
+  unless default['duration'] == '1h'
+    CLIENT.alter_retention_policy('default', db, '1h', 1, true)
   end
-  unless existing.include?('downsampled')
+  unless policy_names.include?('downsampled')
     CLIENT.create_retention_policy('downsampled', db, '7d', 1)
   end
 end