minor #2065 Update macro.rst (dubaaron)

This PR was submitted for the master branch but it was merged into the 1.x branch instead (closes #2065).

Discussion
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Update macro.rst

Small grammar fix: subject-verb agreement "Macros differ" vs "Macros differs"

Commits
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0800545 Update macro.rst

doc/tags/macro.rst

@@ -13,7 +13,7 @@ Here is a small example of a macro that renders a form element:
         <input type="{{ type|default('text') }}" name="{{ name }}" value="{{ value|e }}" size="{{ size|default(20) }}" />
     {% endmacro %}
 
-Macros differs from native PHP functions in a few ways:
+Macros differ from native PHP functions in a few ways:
 
 * Default argument values are defined by using the ``default`` filter in the
   macro body;