minor #2515 Update internals.rst (pribilinskiy)
minor #2515 Update internals.rst (pribilinskiy)

This PR was submitted for the 2.x branch but it was merged into the 1.x branch instead (closes #2515).

Discussion
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Update internals.rst

Missing an opening paren

Commits
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b8967bd3 Update internals.rst

nicolas-grekas/Twig,twigphp/Twig,nicolas-grekas/Twig,nicolas-grekas/Twig,twigphp/Twig,nicolas-grekas/Twig,nicolas-grekas/Twig,twigphp/Twig,gencer/Twig,gencer/Twig