Changed the word "brackets" to "parentheses"

I want to change the word "brackets" to "parentheses" because when I think
of brackets, I think of [], and when I think of parentheses, I think of (),
and when I originally read this, I found the word confusing.

docs/ref/templates/builtins.txt

@@ -419,7 +419,7 @@ will be interpreted like:
 
     if (athlete_list and coach_list) or cheerleader_list
 
-Use of actual brackets in the :ttag:`if` tag is invalid syntax.  If you need
+Use of actual parentheses in the :ttag:`if` tag is invalid syntax.  If you need
 them to indicate precedence, you should use nested :ttag:`if` tags.
 
 :ttag:`if` tags may also use the operators ``==``, ``!=``, ``<``, ``>``,