Copy edit the CHANGELOG

Active Record names has space between the words.

Author: rafaelfranca

activerecord/CHANGELOG.md

@@ -182,10 +182,10 @@
 
 *   Avoid validating a unique field if it has not changed and is backed by a unique index.
 
-    Previously, when saving a record, ActiveRecord will perform an extra query to check for the uniqueness of
-    each attribute having a `uniqueness` validation, even if that attribute hasn't changed.
-    If the database has the corresponding unique index, then this validation can never fail for persisted records,
-    and we could safely skip it.
+    Previously, when saving a record, Active Record will perform an extra query to check for the
+    uniqueness of each attribute having a `uniqueness` validation, even if that attribute hasn't changed.
+    If the database has the corresponding unique index, then this validation can never fail for persisted
+    records, and we could safely skip it.
 
     *fatkodima*