minor #13677 [TwigBundle] add missing asset dependency (nicolas-grekas)

This PR was merged into the 2.7 branch.

Discussion
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[TwigBundle] add missing asset dependency

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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2aead65 [TwigBundle] add missing asset dependency

src/Symfony/Bundle/TwigBundle/composer.json

@@ -17,6 +17,7 @@
     ],
     "require": {
         "php": ">=5.3.9",
+        "symfony/asset": "~2.7|~3.0.0",
         "symfony/twig-bridge": "~2.7|~3.0.0",
         "symfony/http-foundation": "~2.5|~3.0.0",
         "symfony/http-kernel": "~2.7|~3.0.0"