Update twig.rst SymfonyBridgesServiceProvider

Changelog:
2012-05-26: Removed SymfonyBridgesServiceProvider. It is now implicit by checking the existence of the bridge.
minor #903 Update twig.rst SymfonyBridgesServiceProvider (mbutkereit)

This PR was submitted for the 1.1.x-dev branch but it was merged into the 1.1 branch instead (closes #903).

Discussion
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Update twig.rst SymfonyBridgesServiceProvider

Changelog:
2012-05-26: Removed SymfonyBridgesServiceProvider. It is now implicit by checking the existence of the bridge.

Commits
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b8d68e7 Update twig.rst SymfonyBridgesServiceProvider