merged branch tommygnr/fix-docs-batch-filter (PR twigphp#1040)

This PR was merged into the master branch.

Discussion
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Fix filename for batch filter documentation

The documentation on the website for the batch filter currently 404s See: http://twig.sensiolabs.org/doc/filters/batch.html

I believe this is because the filename is incorrect. This PR fixes that.

Commits
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bb05942 Fix filename for batch filter documentation