minor #3027 Add information for when filter filter was added in 2.x…

… branch (YetiCGN)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead (closes #3027).

Discussion
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Add information for when `filter` filter was added in 2.x branch

The current "versionadded" info can be confusing to developers, if they assume 2.9 > 1.41 and don't know that 1.x and 2.x branches are still developed simultaneously.

Commits
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a05da6d Add information for when `filter` filter was added in 2.x branch

doc/filters/filter.rst

@@ -2,7 +2,7 @@
 =========
 
 .. versionadded:: 1.41
-    The ``filter`` filter was added in Twig 1.41.
+    The ``filter`` filter was added in Twig 1.41 and 2.10, if you're on 2.x.
 
 The ``filter`` filter filters elements of a sequence or a mapping using an arrow
 function. The arrow function receives the value of the sequence or mapping: