minor #20096 [TwigBundle] removed unneeded required dep (fabpot)

This PR was merged into the 3.2-dev branch.

Discussion
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[TwigBundle] removed unneeded required dep

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

Commits
-------

6547869 [TwigBundle] removed unneeded required dep

src/Symfony/Bundle/TwigBundle/composer.json

@@ -17,13 +17,13 @@
     ],
     "require": {
         "php": ">=5.5.9",
-        "symfony/asset": "~2.8|~3.0",
         "symfony/twig-bridge": "~2.8|~3.0",
         "symfony/http-foundation": "~2.8|~3.0",
         "symfony/http-kernel": "~2.8|~3.0",
         "twig/twig": "~1.26|~2.0"
     },
     "require-dev": {
+        "symfony/asset": "~2.8|~3.0",
         "symfony/stopwatch": "~2.8|~3.0",
         "symfony/dependency-injection": "~2.8|~3.0",
         "symfony/expression-language": "~2.8|~3.0",