Improve changelog entries in AR

Describe better the changes related to raising errors with empty
array/hash values in where clauses.

[ci skip]

activerecord/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
-*   Change behaviour with empty array in where clause,
-    the SQL generated when  when were passed an empty array was insecure in some cases
+*   Raise `ArgumentError` instead of generating `column IN (NULL)` SQL when
+    empty array is used in where clause value.
 
-    Roberto Miranda
+    *Roberto Miranda*
 
-*   Raise ArgumentError instead of generate invalid SQL when empty hash is used in where clause value
+*   Raise `ArgumentError` instead of generating invalid SQL when empty hash is
+    used in where clause value.
 
-    Roberto Miranda
+    *Roberto Miranda*
 
 *   Quote numeric values being compared to non-numeric columns. Otherwise,
     in some database, the string column values will be coerced to a numeric